Full opinion text
ALARCON, Circuit Judge: In these three companion appeals, appellants F. Thomas Little, Peter R. Chernik, and Harold Grutchfield challenge their convictions for conspiracy to defraud the United States by impeding, impairing, obstructing and defeating the lawful function of the Internal Revenue Service and Department of Treasury in the collection of tax revenue, in violation of 18 U.S.C. § 371. Little, Chernik, and Grutchfield individually and jointly raise numerous issues on appeal. We affirm their convictions. FACTS The indictment in this matter stemmed from an IRS undercover investigation of Indec Financial Inc. (Indec), a real estate development company that sold interests in real estate limited partnerships to investors. Little was the chairman of Indec’s board of directors. Chernik, a member of the California bar, was Indec’s legal counsel. Grutchfield was Indec’s president. Peter Yost, who did not appeal his conviction, was a salesperson for Indec. The IRS investigation commenced on December 24, 1980, when IRS Special Agent Christopher White, posing as Charles Whitman, a representative for a group of investors looking for tax shelters, called Little at Indec regarding a possible investment in a tax shelter. White was referred to Yost. White discussed with Yost the possibility of providing a $200,000 tax shelter for calendar year 1980 for a wealthy client. White stated that he might not be able to contact his client until January 1981. Yost indicated that Indec could accept a check in January 1981. Yost scheduled a meeting with White in Indec’s offices for December 29, 1980. At the December 29 meeting, Yost explained Indec’s investment and shelter programs. According to Yost, Indec had two types of investment programs: one was designed to make a profit and the other was designed to shelter income from taxation. Bedford & Company, a partnership in the Cayman Islands, was of the latter type. Yost explained the Bedford partnership in detail and offered to sell White’s client an interest in Bedford. White again told Yost that he might have difficulty contacting his client before January 1981. Yost assured White that this would not be a problem. Yost explained that the client’s entitlement to a tax deduction depended on his participation in the Bedford partnership prior to June 1, 1980. Because that critical date had already passed, a backdated subscription agreement and promissory note would be used to provide documentary proof that the client was a member of the partnership prior to the June 1, 1980 deadline. The partnership’s records would then reflect that the client’s 1981 check was a delinquent payment on the 1980 promissory note. Yost agreed with White that the client’s accountant and attorneys should not be told of the backdated note. Before the December 29 meeting had ended, Yost gave White several documents, including a Bedford offering memorandum, a blank promissory note to Bedford, and a tax opinion letter regarding Bedford which bore Chernik’s signature. On January 12, 1981, White called Yost at Indee’s offices to discuss the Bedford investment. Yost recommended that White’s client participate in Bedford for three or four years to avoid scrutiny from the IRS. Yost repeated his explanation of the use of the backdated documents and reassured White that his client could take a deduction on his personal tax return for 1980, despite his becoming a member of the Bedford partnership until 1981. Yost further explained that the backdated promissory note would be used only for 1980. For subsequent years of participation in Bedford, White’s client would be billed pri- or to June 1. Yost also emphasized that the IRS would be unable to subpoena Bed-ford’s partnership records because they were maintained in the Cayman Islands. White asked Yost to send him a sample of the documents used for filing the individual partners’ personal tax returns and an outline of the mechanics of Bedford’s investment plan. The copy of the tax schedule Yost sent to White differed from that which Yost had previously indicated should be used. During a subsequent telephone cnversation with Yost, White inquired into this discrepancy. Yost explained that there were some options as to which tax schedule could be used and he would later determine which one White’s client should use to report the deduction from Bedford. On January 22, White went to Indec’s offices to pick up the written explanation of the Bedford investment program and a copy of the schedule his client was to use when filing his individual tax return. The receptionist gave White an envelope which contained an outline of Bedford’s investment plan prepared by Yost and a copy of a schedule E tax form. While White was at Indec’s offices, Little approached White and asked him if he had any questions regarding the investment in Bedford. White responded that he was confused about the mechanics of the investment and how it related to the Bedford offering memorandum. Little told White that the offering memorandum was for purposes of the IRS only. Little also explained that Bedford would prepare the information necessary for White’s client to file his tax return. Little assured White that his client’s privacy would be protected by a numerical filing system. The only documents which would link names to the numbers were secured by an accountant in the Cayman Islands. On February 6, 1981, White and Special Agent Walter Perry, who posed as Vincen-zo Paoli (Paoli), White’s wealthy client, met with Yost, Little, and Chernik to discuss the Bedford investment plan. ' This and subsequent meetings and telephone conversations between IRS agents and Indec representatives were secretly recorded. At the February 6 meeting, Little introduced Chernik as Indec’s attorney and theorist. Little presented to White and Paoli an overview of Indec’s investment programs. Little then elaborated on the specific mechanics of the Bedford partnership investment plan. Little explained that there was an interest in Bedford available for 1980, but in order for Paoli to take a 100% deduction Paoli would have to have entered the partnership before June 1, 1980. Little and Yost assured Paoli that a backdated promissory note would allow him to use Bedford as a deduction for his 1980 individual tax returns and that the IRS would not be able to dispute or disprove that he entered Bedford in May of 1980. Little and Yost also stated that they had successfully used the backdating procedure with other clients. Little advised Paoli not to inform his accountant of the true details of the Bedford deduction because accountants are not privileged. Chernik was present during Little’s presentation of the Bedford partnership and explanation of the use of backdated documents. During the course of the February 6 meeting, Little gave Paoli three copies of a blank subscription agreement and a promissory note to sign. Little encouraged Paoli to sign the Bedford partnership agreement so that he or Chernik could take these documents with them on their upcoming trip to the Cayman Islands. Paoli told the others that he had decided to leave the final decision whether to invest in Bedford up to White. After the meeting concluded, Agent Perry initialed and signed the Bedford subscription agreements and the promissory note under his assumed name, Vincenzo Paoli. Perry gave the signed documents to White. On February 9, White took the signed subscription and promissory note to Indec’s offices. White told Yost and Little that he was uneasy about having to decide whether Paoli should invest in Bedford. Little and Yost reassured White that similar transactions had been successful in the past. Little again emphasized that the dates on the documents could not be disproved, absent a breach from one of the parties involved in the transaction. Little left the meeting and Yost continued speaking with White. Yost showed White two client files containing backdated promissory notes and offered to contact one of these clients. The client told White that he was satisfied with the backdating method. Yost’s client also told White that he had been given backdated dunning letters. Yost assured White that dunning letters could be provided to Paoli if he wanted them. Yost also emphasized the secrecy regarding the files on Paoli’s investment in Bedford. White left Indec’s office and later that evening called Yost to inform him that he had advised Paoli not to invest in Bedford. On February 18, White returned Yost’s call and briefly conversed with him. This was White’s last contact with Indec personnel. The undercover operation was suspended for several months because of the unavailability of government funds for the investigation. IRS agents resumed the undercover investigation of Indec in August 1981. On August 27, 1981, Agent Perry, acting as Paoli, called Yost and asked whether Indec still had any tax shelters available for 1980. Yost indicated that such a shelter was available and arranged a meeting for September 21. On September 21, 1981, Paoli and another IRS special agent posing as Joe Russo, met with Yost, Little, Chernik, and Grutch-field at Indec’s new office. Paoli then explained why he had not contacted Indec since February. Paoli stated that he had until October 15, 1981, to file his 1980 tax return. Little asked Paoli if he needed any deductions for 1980 and Paoli replied that he could use $200,000 in deductions. Little and Grutchfield indicated that they had some writeoffs that were available. Little offered Paoli the same type of tax shelter in Bedford he had described to him in February. Little indicated that a backdated subscription agreement and promissory note would be used. After Little left the September 21, 1981 meeting, Grutchfield, Chernik, and Yost explained to Paoli and Russo that the backdated promissory notes would document Paoli’s status as a partner in Bedford prior to June 1, 1980. They also agreed that fraudulent dunning letters could be placed in Paoli’s file to document further his entry into the partnership prior to June 1, 1980. Grutchfield stressed that the letters would “make things look better” and that Paoli should not let the IRS learn of the backdating of the notes. Before the meeting ended, Paoli stated that he would accept the offer to invest in Bedford in order to take the investment as a writeoff on his 1980 returns.- Paoli signed a promissory note which Yost had backdated to May 21, 1980. Russo asked that dunning letters be provided. On October 7, Paoli and Russo met with Yost, Little, Grutchfield, and Chernik in Little’s office at Indec in order to conclude the Bedford transaction. At the meeting, Little gave Russo four fraudulent dunning letters. Russo then paid Little for the interest in Bedford by placing a cashier’s check for $100,000 on his desk. As the group prepared to celebrate the conclusion of the transaction with champagne, several IRS special agents entered the office. Some agents arrested Yost, Grutchfield, and Little in Little’s office. Other agents arrested Chernik in Indec’s reception area. The agents took Yost, Grutchfield, Little, and Chernik to San Francisco for arraignment. A team of special agents remained at Indec’s offices from the time of the arrest on October 7 through shortly after noon on October 8. The parties dispute whether the agents searched the office. DISCUSSION I. Legality of the Retroactive Allocation A. IRS Statutes and Regulations Appellants urge us to reverse their convictions for conspiracy to defraud the government on the ground that the retroactive allocation to Paoli of Little’s and Grutchfield’s shares of the Bedford partnership losses was legal. They contend that the interplay between 26 U.S.C. §§ 704(a), 761(c) and 6031, as they read it at the time of the Bedford transaction, permitted the retroactive allocation to a new partner of partnership losses attributable to periods prior to the new partner’s entry into the partnership. Specifically, they contend that pursuant to these code sections and respective regulations, Bed-ford’s partnership agreement could have been amended at any time prior to October 15, 1981, to effect a legal retroactive allocation of Little’s and Grutchfield’s shares of Bedford’s 1980 losses to Paoli. Appellants are wrong. Their tortured interpretation of the pertinent statutes and legislative history does not withstand scrutiny. Appellants and the government agree that 26 U.S.C. § 706(c)(2)(A), which governs the sale of a partner’s entire interest in a partnership, applies to the transaction in this case. Section 706(c)(2)(A) provides in relevant part: The taxable year of a partnership shall close— (i) with respect to a partner who sells or exchanges his entire interests in a partnership, and ... Such partner’s distributive share of items described in section 702(a) for such year shall be determined, under regulations prescribed by the Secretary, for the period ending with such sale, exchange, or liquidation. The pertinent regulation, 26 C.F.R. § 1.706-l(c)(2)(ii), provides that when a partner sells his or her entire interest, the partnership’s taxable year closes with respect to that partner on the date of the sale, and the transferor partner must report his or her share of the partnership’s gains or losses attributable to the period prior to the sale. The transferee partner must report his or her share of the partnership’s gains or losses attributable to the period after the sale. See 1 McKee, Nelson and Whitmire, Federal Taxation of Partnerships and Partners §§ 11.02[3], [4][a], 5[a] at 11-6 to 11-11 (1977 ed.); 2 Willis, Pennell, and Postlewaite, Partnership Taxation § 87.04 at 87-10 (3rd ed. 1981). In Moore v. Commissioner, 70 T.C. 1024 (1978), although the issue before the court involved retroactive allocations under 26 U.S.C. § 706(c)(2)(B), the tax court expressly noted that 26 U.S.C. § 706(c)(2)(A) and 26 C.F.R. § 1.706-l(c)(2)(ii), require a partner who transfers his entire interest to report his distributive share of partnership items for the period he was a partner. The court emphasized that the partner could not transfer retroactively those items to the transferee by modifying the partnership agreement under 26 U.S.C. § 761(c). Id. at 1031. In light of the express language in Moore, retroactive allocations in situations governed by 26 U.S.C. § 706(c)(2)(A) cannot be legally accomplished by amending the partnership agreement under 26 U.S.C. § 761(c). Smith v. Commissioner, 331 F.2d 298 (7th Cir.1964), is not to the contrary. Smith involved the sale of an entire partnership interest between two existing, equal partners. Although the sale occurred in the middle of the partnership’s taxable year, the partners amended the partnership agreement, at the time of the sale, to allocate substantially all of the fiscal year’s gains and losses to the purchasing partner. After finding that there was no evidence that the partners modified the partnership agreement in order to avoid or evade taxes, the Seventh Circuit concluded that the retroactive allocation of the partnership income was proper. Smith clearly does not support the proposition urged by appellants — that retroactive allocations to new transferee partners in § 706(c)(2)(A) situations are allowed. See also Rodman v. Commissioner, 542 F.2d 845, 857-58 (2nd Cir.1976). (The Second Circuit distinguished cases such as Smith where existing members of an ongoing partnership agreed to rearrange shares retroactively from cases where a new partner has joined the partnership by a transfer of partnership interest. The Second Circuit found that retroactive reallocation where a new partner has joined the partnership was prohibited. The Second Circuit also concluded that when one partner sold his entire interest to the remaining three partners, “the partnership year closed as to him and his distributive shares ... were set as of that moment.”) In 1976, Congress amended 26 U.S.C. § 706(c)(2)(B) in order to make clear that retroactive allocations were not permitted where new partners entered into a partnership by contribution or acquisition of less than the entire interest of an existing partner. Appellants contend that because the 1976 amendments did not affect § 706(c)(2)(A), retroactive allocations continued to be permissible under the latter section. They assert that if Congress had wanted to bar retroactive allocations under § 706(c)(2)(A), it would have done so under the 1976 Tax Reform Act. This argument is based on appellants’ unreasonable and erroneous contention that retroactive allocations were permissible under § 706(c)(2)(A). A reading of the legislative history of the 1976 amendment to § 706(c)(2)(B), clearly indicates that Congress was aware that retroactive allocations were not permissible under § 706(c)(2)(A). In explaining the reasons for the amendment to § 706(c)(2)(B), the committee reports: “Present law is not clear whether retroactive allocations are permissible under the Internal Revenue Code. Essentially, there are four partnership Code provisions which have a direct or indirect bearing on this issue — sections 704(a), 761(c), 704(b)(2), and 706(c)(2)(B).” H.R.Rep. No. 658, 94th Cong., 1st Sess.; S.Rep. No. 938, 94 Cong., 2d Sess.; reprinted in 1976 U.S.Code Cong. & Ad. News 2897, 3017 & 3531. The omission of § 706(c)(2)(A) from this enumeration was not an oversight by Congress. Congress emphasized that it was amending § 706(c)(2)(B) to clarify that retroactive allocations were not permitted under this section and to make it consistent with the requirements of § 706(c)(2)(A) and its respective regulation, 26 C.F.R. § 1.706-1(c)(2)(H). Id. at 3018-19 & 3532-34. Specifically, the committee report states: The bill amends present law (sec. 706(c)(2)(B)) to make it clear that the varying interests rule of this provision is to apply to any partner whose interest in a partnership is reduced, whether by sale, exchange, or otherwise, such as by the admission of a new partner who purchased his interest directly from the partnership. Correspondingly, the provision is to apply to the incoming partner so as to take into account his varying interests during the year. In addition, regulations are to apply the same alternative methods of computing allocations of income and loss to situations falling under section 706(c)(2)(B) as that currently provided with respect to section 706(c)(2)(A) situations (sale or liquidation of an entire interest). Id. at 3019 (emphasis added); see also id. at 3533-34. The purpose of the amendment to § 706(c)(2)(B) was not to modify the existing law, as appellants suggest, but to clarify it so that it would be applied consistently. See Richardson v. Commissioner, 76 T.C. 512, 523-24 (1981), aff’d, 693 F.2d 1189 (5th Gir.1982). The legislative history of the 1976 Tax Reform Act clearly indicates that Congress did not amend § 706(c)(2)(A) to bar retroactive allocations because there was no need to do so. Retroactive allocations to new partners were not permitted under that section. Furthermore, the legislative history of the 1976 Tax Reform Act also refutes appellants’ assertion that the interplay between 26 U.S.C. §§ 704(a) and 761(c) allows for retroactive allocation in § 706(c)(2)(A) situations. Congress noted that this same argument had been made in order to circumvent the prohibition against retroactive allocations under § 706(c)(2)(B). To reinforce the prohibition against retroactive allocations, Congress amended § 704(a). The committee report states: In addition, the present law provision relating to the effect of a partnership agreement (sec. 704(a)) is amended to provide that it is overridden by any contrary provisions of the partnership provisions (under subchapter K, including section 706(c)(2)(B)). Thus, a partnership agreement, amended (pursuant to section 761(c)) to provide for a retroactive allocation, will not override an allocation required under section 706(c)(2)(B). 1976 U.S.Code Cong. & Ad.News at 3020; see also id. at 3534. Section 704(a) was amended to read: “A partner’s distributive share of income, gain, loss, deduction or credit shall, except as otherwise provided in this chapter, be determined by the partnership agreement” (emphasis added). Congress thereby made clear that a partnership agreement amended pursuant to § 761(c) could not override an allocation required under § 706(c)(2)(B). Id. at 3020 & 3534. See Marriott v. Commissioner, 73 T.C. 1129 (1980); Moore v. Commissioner, 70 T.C. 1024 (1978). This amendment to § 704(a) also resolved any doubt regarding § 706(c)(2)(A). A partnership agreement amended pursuant to § 761(c), would not override the allocation mandated by § 706(c)(2)(A). In sum, at the time of the initiation of the Bedford deal on December 24,1980, the allocation rule set forth in § 706(c)(2)(A), as interpreted by case law and clearly reflected in the pertinent legislative history, was and remains mandatory. The requirements of § 706(c)(2)(A) cannot be circumvented by modifying the partnership agreement under § 761(c). B. Jury Instructions Closely related to appellants’ claim that retroactive allocation was allowed under 26 U.S.C. § 706(c)(2)(A), is their challenge to the district court’s jury instructions. Appellants argue that the district court committed reversible error by: (1) failing to give some of the joint and individual instructions they requested, (2) giving some of the government’s instructions, and (3) deleting parts of some of the government’s instructions. Initially, we note that a trial judge is given substantial latitude in tailoring jury instructions as long as they fairly and adequately cover the issues presented. United States v. Marabelles, 724 F.2d 1374, 1382-83 (9th Cir.1984). In United States v. Smith, 735 F.2d 1196 (9th Cir.1984), this court recently reiterated the standard of review we apply to challenges to jury instructions. “The adequacy of a judge’s instructions to the jury is measured by reading the instructions as a whole. The judge’s formulation of those instructions or his choice of language is entirely in his discretion, so long as the instructions fairly and adequately cover the issues presented.” Id. at 1198 (citation omitted). Our review of the jury instructions in this case, convinces us that there was no abuse of discretion. The district court instructed the jury as follows: Now the law provides that a taxpayer who is in a partnership shall take into account his share of the partnership losses for the taxable year, or portion thereof, in which he is a partner in determining his individual taxable income. However, the law prohibits a partner from taking into account, in determining his individual taxable income, a share of the partnership losses for a taxable year, or a portion thereof, prior to his admission into the partnership. In evaluating the presence or absence of specific intent, you may consider, together with all the other evidence in the case, the circumstance that no decided case directly and precisely construes the legality of a transaction such as that alleged to be the substance of the alleged conspiracy in this case. If a partner sells or exchanges his entire partnership interest, the partnership’s taxable year closes, with respect to him, on the date of the sale or exchange. The date selected by the parties should control provided the benefits and burdens shift on that date. The law permits the modification of a partnership agreement which is agreed to by all the partners or as modified in any manner which is provided to the partnership agreement with respect to any taxable year of the partnership until the date prescribed by law for filing of a partnership tax return for such taxable year, and the law as of October 7, 1981, provided that a partnership need not file any partnership tax return for any year in which the partnership carried on no business in the United States, and derived no income from sources within the United States. Now if you find that a defendant reasonably believed that the sale or assignment of his entire partnership interest in 1981, after the close of the calendar year 1980, was permissible under the Internal Revenue Code, even if the transaction was not valid under the Internal Revenue Code, then such a defendant cannot have entertained the required specific intent under the conspiracy law, and is entitled to acquittal. The district court’s instructions gave an accurate statement of the applicable law and accommodated the appellants’ defense theory that they reasonably believed that the proposed Bedford transaction was legal. C. Reliance on Dahlstrom Appellants contend that reversal of their convictions is required in light of this court’s opinion in United States v. Dahlst-rom, 713 F.2d 1423 (9th Cir.1983), cert. denied, — U.S. —, 104 S.Ct. 2363, 80 L.Ed.2d 835 (1984). Appellants’ reliance on Dahlstrom is misplaced. The defendants in Dahlstrom were convicted of conspiracy to defraud the government by impeding, impairing, and obstructing the IRS in the ascertainment, computation, assessment and collection of income taxes and of aiding and abetting the preparation of false returns because of their involvement in promoting a tax shelter program which involved the creation of a foreign trust organization. The court concluded that reversal of the defendants’ convictions was required on several grounds. First, we emphasized that “[d]ue process requires that a person be given fair notice as to what constitutes illegal conduct so that he may conform his conduct to the requirements of the law.” Id. at 1427. In Dahlstrom, on the dates alleged in the indictment, there was no statute that expressly made illegal the type of tax shelters promoted by the defendants nor was there any case law which held that defendants’ scheme lacked economic substance for tax purposes. Thus, the defendants could not have had “fair notice” that their conduct was illegal. Second, the court noted that where a defendant is not given fair notice of the requirements of the law, a defendant necessarily lacks the requisite intent to violate the law. In the present case, as discussed above, the law regarding the legality of retroactive allocations under § 706(c)(2)(A) was clear on the dates alleged in the indictment. Case law and relevant legislative history made plain that the retroactive allocation to a new partner of partnership losses attributable to periods prior to the new partner’s entry into the partnership was impermissible. Appellants had fair notice of the law and they could have conformed their conduct to the requirements of the law. Thus, they could have had the requisite intent to violate the law. Because the law regarding retroactive allocations of a partner’s interest in a partnership was clear and appellants had fair notice as to what constituted illegal conduct, we also reject appellants’ contention that their convictions violated their due process rights or the constitutional prohibition against ex post facto laws. Appellants also rely heavily on Dahlstrom to support their assertion that the prosecution violated their first amendment rights of commercial free speech. In Dahlstrom, this court noted that the first amendment barred prosecution for advocacy of conduct which did not violate existing law. Unlike Dahlstrom, the record in this case indicates that the appellants’ conduct was prohibited by existing law. Appellants encouraged Paoli to enter into the Bedford partnership so he could deduct from his personal return losses to which he was not entitled. They developed and presented a scheme as to how Paoli could retroactively declare the losses on his 1980 tax return. They supplied Paoli with backdated and fraudulent documents which would substantiate the claimed deductions in the event of an IRS audit, and told him they had used the backdating scheme in the past. Appellants’ conduct consequently went far beyond advocacy and amounted to participation in unlawful action. Appellants cannot cloak their intentional misconduct under the protections of the first amendment. II. Suppression Claims A. Tape Recordings Relying on People v. Conklin, 12 Cal.3d 259, 114 Cal.Rptr. 241, 522 P.2d 1049, appeal dismissed, 419 U.S. 1065, 95 S.Ct. 652, 42 L.Ed.2d 661 (1974), appellants contend that the tape recordings of the conversation between the IRS undercover agents and appellants violated their fourth amendment rights and Cal.Penal Code § 632, which prohibits electronic eavesdropping without the consent of all the parties to the communication. Therefore, appellants argue that the district court should have suppressed the tapes. We have previously considered and rejected such arguments. We do so again. In this circuit, the rule regarding admissibility of evidence in a federal prosecution is clear and simple. Evidence obtained in violation of neither the Constitution nor federal law is admissible in federal court proceedings without regard to state law. See United States v. Adams, 694 F.2d 200, 201-02 (9th Cir.1982), cert. denied, 462 U.S. 1118, 103 S.Ct. 3085, 77 L.Ed.2d 1347 (1983) (citing United States v. Hall, 543 F.2d 1229, 1234-35 (9th Cir.1976) (en banc), cert. denied, 429 U.S. 1075, 97 S.Ct. 814, 50 L.Ed.2d 793 (1977); United States v. Keen, 508 F.2d 986, 989 (9th Cir.1974), cert. denied, 421 U.S. 929, 95 S.Ct. 1655, 44 L.Ed.2d 86 (1975)). The tape recordings in the present case were not obtained in violation of the fourth amendment. See United States v. White, 401 U.S. 745, 751-53, 91 S.Ct. 1122, 1125-27, 28 L.Ed.2d 453 (1971). The fourth amendment does not afford protection to wrongdoers’ misplaced confidences. Hoffa v. United States, 385 U.S. 293, 302, 87 S.Ct. 408, 413, 17 L.Ed.2d 374 (1966). Nor were the tape recordings obtained in violation of federal law. Under 18 U.S.C. § 2511(2)(c), the tape recordings were lawful and, thus, were admissible under federal law. 18 U.S.C. § 2517(3). We also reject the attempt by appellants to bypass this clear rule by invoking the supervisory power of the district court. The supervisory power is to be applied with caution when the result of its application would be to exclude probative evidence. See United States v. Payner, 447 U.S. 727, 734-35, 100 S.Ct. 2439, 2445-46, 65 L.Ed.2d 468 (1980). We decline to apply it here, where there has been no outrageous conduct by the agent and no violation of any appellants’ federal rights. B. 18 U.S. C. § 3109 Appellants argue that the IRS agents violated the “knock and notice” requirement of 18 U.S.C. § 3109, by failing to give notice of their authority and purpose prior to arresting the appellants in Indec’s office. Appellants contend that “all evidence obtained” from their arrest and subsequent search of Indec’s offices must be suppressed. The government asserts, and appellants do not refute, that the only post-arrest evidence introduced at trial were statements made by Yost and Chernik. Appellants cannot complain about the introduction of Yost’s statements. The district court carefully instructed the jury to consider Yost’s statements only against him. Moreover, appellants may not vicariously assert Yost’s fourth amendment rights. See Rakas v. Illinois, 439 U.S. 128, 138, 99 S.Ct. 421, 427, 58 L.Ed.2d 387 (1978); Alderman v. United States, 394 U.S. 165, 171-72, 89 S.Ct. 961, 965-66, 22 L.Ed.2d 176 (1968). Accordingly, we need only concern ourselves with the post arrest' statements made by Chernik. Under 18 U.S.C. § 3109, a federal officer may break open “any outer or inner door” to execute a search warrant if after notice of authority and purpose, entrance is refused. This section also applies to an arrest, with or without a warrant, by a federal officer for a federal offense. Sabbath v. United States, 391 U.S. 585, 588, 88 S.Ct...1755, 1757, 20 L.Ed.2d 828 (1968); United States v. Crawford, 657 F.2d 1041, 1044 (9th Cir.1981). The enforcement of section 3109 serves three interests: (1) it provides protection from violence, assuring the safety and security of both the occupants and the entering officers; (2) it protects an individual’s right to privacy; and (3) it protects against the needless destruction of private property. United States v. BustamanteGomez, 488 F.2d 4, 9-10 (9th Cir.1973), cert. denied, 416 U.S. 970 (1974). Here, the IRS agents conceded that they did not knock and announce their presence or purpose before entering Indec’s office. In light of this concession and by allowing Chernik’s statements into evidence, the district court must have determined that § 3109 was inapplicable to the agents entry into Indec’s offices. We limit our review to the entry into the reception area. Whether we review the district court’s determination under the clearly erroneous standard, or under the de novo standard, we conclude that the district court was correct. The IRS agents entered Indec’s reception area through an unlocked door during business hours. Chernik was in Indec’s reception area when the agents arrested him. A reception area is used for purposes of greeting and screening those who enter an office to determine if the individual is properly there. Also, office workers are generally free to walk through this area. Since the public and office workers are allowed to walk freely into a reception area, an individual working in the office can have no reasonable expectation of privacy there. Accordingly, section 3109 does not apply to Indec’s reception area. Appellants cite Wong Sun v. United States, 371 U.S. 471, 83 S.Ct. 407, 9 L.Ed.2d 441 (1963); Lo-Ji Sales, Inc. v. New York, 442 U.S. 319, 99 S.Ct. 2319, 60 L.Ed.2d 920 (1979); and United States v. Phillips, 497 F.2d 1131 (9th Cir.1974), in support of their claim that § 3109 should apply to this situation. Appellants’ reliance on these cases is misplaced. Neither Wong Sun nor Lo-Ji Sales, Inc., involved § 3109. The issue before the court in Wong Sun was whether the police had probable cause to arrest the defendants. In Lo-Ji Sales, Inc., the Supreme Court did not address the propriety of the police officer’s entry into an adult bookstore during business hours to effectuate a search warrant. The issue in Lo-Ji was the sufficiency of an affidavit and search warrant to seize certain items once the officers were on the business premises. United States v. Phillips, is factually distinguishable. Phillips involved a nocturnal entry into a locked, occupied business. In concluding that § 3109 applied to such an entry, this court emphasized that “a locked commercial establishment, at least at night, is a ‘house’ as that word is used in § 3109.” 497 F.2d at 1133-34. C. Unlawful Search oflndec Appellants also argue that “all fruits” of the IRS agents’ search of Indec’s offices should have been suppressed. We agree with the government that we need not reach this issue. Other than the post-arrest statements of Yost and Chernik, which we have discussed above, none of the alleged fruits of the search and seizure of Indec’s offices was introduced into evidence at appellants’ trial. III. IRS Authority for Undercover Investigation and Government Misconduct Appellants contend that reversal of their convictions is required because the IRS agents acted beyond their statutory authority in conducting the undercover investigation and committed numerous instances of alleged misconduct. We reject both of these contentions. A. IRS Authority to Conduct Undercover Investigation Appellants contend that the IRS agents exceeded their statutory authority by conducting the undercover investigation and therefore the entire investigation must be ruled void and unlawful. Appellants fail to cite any case which directly supports their contention that IRS undercover criminal investigations exceed the IRS’s statutory authority. Our review of the relevant statutes convinces us that the IRS undercover criminal investigations such as the investigation in this case are well within the broad authority Congress delegated to the agency. Under 26 U.S.C. § 6301, Congress granted the IRS broad authority to collect taxes. Congress also gave the IRS a broad mandate to investigate all persons who may be liable for any internal revenue tax, 26 U.S.C. § 7601, and broad discretion in determining what “reasonable devices or methods” may be “necessary or helpful” in collecting revenue tax. 26 U.S.C. § 6302(b). Under 26 U.S.C. § 7608(b), Congress granted police powers to IRS criminal investigators. These statutory grants of authority are clearly broad enough to encompass undercover criminal investigations which may be necessary and proper to the determination and collection of taxes, and to the general enforcement of the revenue laws. Furthermore, the Supreme Court has recognized that in order to apprehend individuals engaged in criminal activities, the government is entitled to use decoys and to conceal the identity of its agents. Lewis v. United States, 385 U.S. 206, 208-09 & n. 5, 87 S.Ct. 424, 425-26 & n. 5, 17 L.Ed.2d 312 (1966). Indeed the Supreme Court expressly stated that “there are circumstances when the use of deceit is the only practicable law enforcement technique available.” United States v. Russell, 411 U.S. 423, 436, 93 S.Ct. 1637, 1645, 36 L.Ed.2d 366 (1973) (rejecting entrapment defense where undercover agent supplied defendant with chemical necessary to manufacture illegal drug). This case, where the collection of taxes is being impeded by fraudulent conduct, presents such circumstances. See, e.g., United States v. Everett, 692 F.2d 596 (9th Cir.1982), (IRS undercover investigation revealed defendants’ scheme to sell tax shelter investments that had been backdated to allow buyers to claim deductions on their federal income tax returns for the years prior to those in which transaction actually occurred). Appellants’ contention that the IRS agents’ undercover investigation in this case was prohibited by 26 U.S.C. § 7214(a)(4), (a)(5) and (a)(6), is patently frivolous. The agents’ conduct was simply part of their undercover role. Were we to accept appellants’ contention that the agents’ conduct violated § 7214 we would, in effect, be barring undercover investigations in which a federal agent must pretend and appear to violate the law. Clearly, Congress could not have intended such a rule in enacting § 7214. Moreover, even if the IRS agents violated § 7214, the remedy lies not in freeing appellants, but in prosecuting the agents. See Hampton v. United States, 425 U.S. 484, 490, 96 S.Ct. 1646, 1650, 48 L.Ed.2d 113 (1976). Because the IRS agents acted within their authority in conducting the undercover investigation, we also reject appellants’ argument that the undercover investigation violated appellants’ due process rights. B. IRS Agent Misconduct Appellants allege numerous instances of misconduct by the IRS agents which appellants claim require reversal of their convictions, either under the due process clause or this court’s supervisory powers. Our review of the record convinces us that none of the allegations of government misconduct requires reversal. 1. Affirmative Misrepresentation by IRS Agent Perry Appellants argue that the district court should have suppressed the tapes of all of the conversations between appellants and the IRS agents occurring after August 24, 1981, because they were secured by “fraud, deceit and trickery.” Their argument is based on Agent Perry’s denial to an Indec receptionist that he was with the IRS. Appellants assert that Perry had a duty to answer truthfully when questioned about his affiliations. Appellants further contend that if Agent Perry had answered truthfully, they would have terminated their dealings with the IRS agents. Appellants fail to cite any cases holding that an undercover agent is under an affirmative duty to respond truthfully if questioned about his or her true identity. The cases relied on by appellants all involve government agents — known by the sus-peets to be agents — who through deceit, trickery or misrepresentation abused the powers of their position to gain access to a private citizen’s premises or records. The rule set forth in those cases is that access gained by a government agent, known to be such by the person with whom the agent is dealing, violates the fourth amendment's bar against unreasonable searches and seizures if such entry was acquired by affirmative or deliberate misrepresentation of the nature of the government’s investigation. This rule is inapplicable to cases, such as the present, involving an undercover agent’s denial that he or she is a federal agent. In Jones v. Berry, 722 F.2d 443 (9th Cir.1983), cert. denied, — U.S.—, 104 S.Ct. 2343, 80 L.Ed.2d 817 (1984), we recognized that cases such as those relied on by appellants are readily distinguishable from situations such like the present, where “IRS agents did not pretend to be civil agents, thereby implicitly invoking their powers as civil investigators, when in fact they intended to conduct a criminal investigation. Rather, the agents pretended to be fellow criminals in order to gain the [suspect taxpayer’s] confidence.” Id. at 447 n. 5. The undercover agent’s denial of association with the government is justifiable and necessary to protect the agent’s “cover.” Were we to accept appellants’ theory, we would, in effect, put an end to federal undercover operations by imposing a duty on federal undercover agents to identify themselves as such whenever they are asked. To insure themselves against convictions based on evidence obtained through undercover investigations, criminals would only have to ask their acquaintances and associates if they were government agents. We reject appellants’ fanciful theory. 2. Witness Intimidation Appellants allege that the IRS intimidated their expert witness into not testifying on surrebuttal. They contend that this alleged government misconduct amounted to a denial of their due process rights. Appellants also urge us to apply our supervisory powers to reverse the conviction and to order the district court to dismiss the indictment. In support of their claim of witness intimidation, appellants rely on a line of cases which support the proposition that substantial government interference with a defense witness’s free and unhampered choice to testify amounts to a violation of due process. See Webb v. Texas, 409 U.S. 95, 97-98, 93 S.Ct. 351, 353-354, 34 L.Ed.2d 330 (1972) (defense witness intimidated into not testifying by remarks of trial judge); Washington v. Texas, 388 U.S. 14, 19, 87 S.Ct. 1920, 1923, 18 L.Ed.2d 1019 (1967) (right to present witness to establish defense is fundamental to due process); United States v. Goodwin, 625 F.2d 693, 703 (5th Cir.1980); and United States v. Hammond, 598 F.2d 1008, 1012-15 (5th Cir.1979) (defense witnesses intimidated by FBI agent during court recess and by subpoena to appear before a grand jury); United States v. Henricksen, 564 F.2d 197, 198 (5th Cir.1977) (defense witness intimidated by terms of codefendant’s plea bargain); United States v. Morrison, 535 F.2d 223, 226-28 (3rd Cir.1976) (defense witness intimidated by prosecutor’s remarks); United States v. Thomas, 488 F.2d 334, 335-36 (6th Cir.1973) (defense witness intimidated by remarks of secret service agent during court recess). Whether substantial government interference with a defense witness occurred is a factual determination to be made by the trial court. See United States v. Goodwin, 625 F.2d at 703; United States v. Bates, 600 F.2d 505, 511 (5th Cir.1979). We review a district court’s factual determination under the clearly erroneous standard. The testimony adduced at the lengthy hearing on the motion to dismiss held on the witness intimidation claim revealed the following pertinent facts. On October 6, 1982, the government learned that the following day appellants would call as an expert witness Richard Losey, a law school professor and practitioner specializing in tax law. Losey was to testify in support of appellants’ theory regarding the legality of the retroactive allocations under 26 U.S.C. § 706(c)(2)(A). Prosecution attorneys became curious about Losey’s relationship with Chernik. An IRS special agent offered to inquire into the matter. On the morning of October 7, the special agent called the IRS office and asked whether anyone had information regarding Losey. The special agent’s supervisor instructed another agent to call Losey’s office and gather some information. The agent called Losey’s office, identified himself as “Mr. Jacobs,” and asked for Chernik. A secretary informed the agent that no one by that name worked at the firm. The agent asked the secretary if Chernik was a partner at the firm. The secretary responded that he was not. The agent also asked the secretary if Losey and Chernik were on the faculty at the same law school. The agent told the secretary that he had been referred to the firm by a friend of Chernik. The agent then made further inquiries into the firm’s practice. Before ending the conversation, the agent left a number where Losey could return the call. Losey stated that his secretary informed him about the peculiar call on the morning of October 8, the day after he testified as an expert. Losey claimed that he was chilled by the suspicious phone call because he suspected government involvement. Lo-sey immediately informed one of the defense counsel of the .call and told him he would not “feel like one hundred percent” on the stand. Losey further testified that when it was confirmed that the caller was from the IRS, he felt intimidated and feared reprisals. Thus, Losey asserted that the call affected his decision whether to testify on surrebuttal. Losey also testified, however, that the source of the call was not confirmed until the evening of October 11. Losey testified that he was told by one of the defense counsel on October 9 that the defense lawyers had reached a consensus not to have him testify on surrebuttal. Counsel for appellant Grutchfield testified that he wanted Losey to testify on surrebuttal on the “international tax law aspects” of the case. Counsel decided against calling Losey to the stand after he confirmed the caller’s true identity because he believed Losey was too nervous. We may infer from the district court’s denial of the motion to dismiss based on appellants’ witness intimidation claim that the district court found that there was no government misconduct. The district court expressly noted that a simple phone call to investigate the connection between Losey and Chernik did not amount to intimidation. We agree with the district court. The only evidence of “intimidation” presented by appellants was a telephone call made by an IRS agent to Losey’s office. The purpose of the call was to investigate into the relationship between Losey and Chernik. We note that there is nothing improper with investigation of trial witnesses. Indeed, such investigations are often necessary to collect information for cross-examination or impeachment purposes. A telephone call is an appropriate means to conduct such an investigation. In this case, the fact that the IRS agent who placed the call to Losey’s office concealed his true identity does not amount to government misconduct. We also note that there was no evidence presented that the IRS made the call in order to intimidate Losey. Moreover, although Losey testified that the call made him nervous, he never stated that he would not testify if called on surrebuttal. On these facts, we cannot find any evidence of witness intimidation by the government. Thus, our review of the record convinces us that the district court’s finding on the witness intimidation claim was not clearly erroneous and that the district court properly denied the motion to dismiss. 3. Alleged CIA Involvement Appellants argue that their convictions should be reversed because the Central Intelligence Agency was involved in the IRS’s investigation of Indee and its personnel. Alternatively, appellants seek a remand of this case for a hearing on the alleged CIA involvement. After a closed hearing on appellants’ motion for dismissal of the indictment based on alleged CIA involvement in this case, the district court rejected appellants’ claim of CIA involvement and denied the motion to dismiss. The transcript of this hearing was submitted under seal to this court. Our review of the transcript convinces us that the district court properly rejected the claim of CIA involvement and denied the motion to dismiss. On appeal, appellants continue to insist that the CIA was involved in this case. Appellants have attempted to prove their allegation through the numerous documents lodged with this court. The documents submitted by appellants are wholly outside the record properly before this court. We must limit our review of appellants’ claim to the record that was made before the trial court. See Fed.R.App.P. 10(a); Retana v. Apartment, Motel, Hotel & Elevator Operators Union, 453 F.2d 1018, 1027 (9th Cir.1972). 4. Brady Material Appellants further assert that the government’s failure to provide them with the purportedly exculpatory statements of Amoldo Rodriguez mandates reversal of their convictions under Brady v. Maryland, 373 U.S. 83, 83 S.Ct. 1194, 10 L.Ed.2d 215 (1963). Alternatively, appellants contend that reversal is required because the government perpetuated a fraud on the court. We find no Brady violation or fraud upon the court in this case. Under Brady, the prosecution may not suppress exculpatory evidence that is material to the issue of guilt or punishment. Id. at 87, 83 S.Ct. at 1196. In a case, such as the present, where a general request for exculpatory evidence is made, “the test for materiality is whether the suppressed evidence ‘creates a reasonable doubt that did not otherwise exist.’ ” United States v. Gardner, 611 F.2d 770, 774 (9th Cir.1980) (quoting United States v. Agurs, 427 U.S. 97, 112, 96 S.Ct. 2392, 2401, 49 L.Ed.2d 342 (1976); accord United States v. Cadet, 727 F.2d 1453, 1467-68 (9th Cir.1984)). However, in response to a request for exculpatory evidence, the prosecution does not have a constitutional duty to disclose every bit of information that might affect the jury’s decision; it need only disclose information favorable to the defense that meets the appropriate standard of materiality. United States v. Gardner, 611 F.2d at 774-75. Rodriguez told IRS agents that Bedford’s Central American real estate holdings were nonexistent except on paper. Rodriguez stated that he prepared the fraudulent paperwork and forwarded it to Indec. Although this information was not used at trial, it was included in the government’s sentencing report. These statements are clearly not exculpatory. After trial and sentencing, counsel for Grutchfield interviewed Rodriguez in Costa Rica. In declarations dated April 28, 1983, Rodriguez states that IRS agents chained him to a chair, coached him as to his answers, and compelled him to give the answers they wanted to hear. He further stated that Grutchfield had no knowledge about the true status of Bedford and its assets and that on several occasions he told the IRS agents of Grutchfield’s ignorance on this point. Based on these latter declarations of Rodriguez, appellants assert that there was a Brady violation. The April 28 declarations of Amoldo Rodriguez are not properly before us. Considering the record that is properly before us, we find no Brady violation or fraud upon the court in this case. 5. Remaining Allegations of Government Misconduct Appellants also point to other instances of alleged government misconduct. We have already discussed the search and seizure of Indec’s office. The remedy for any fourth amendment violation is suppression of the tainted evidence. However, other than Chernik’s and Yost’s post arrest statements, no evidence obtained subsequent to the arrests was introduced at trial. Appellants also claim that the government improperly threatened a prospective witness in order to have him testify at their trial. Appellants assert that the threat “appears” to be a violation of 18 U.S.C. § 872. Appellants clearly lack standing to assert the witness’s rights. Relying on United States v. Stahl, 616 F.2d 30 (2d Cir.1980), appellants argue that the prosecutor’s references to money and greed as appellants’ motivation for the conspiracy amounted to prejudicial error. The present case is readily distinguishable from Stahl. In Stahl, the prosecutor’s trial strategy “included a[n] ... appeal to class prejudice.” Id. at 33. The prosecutor, therefore, engaged in “calculated and persistent efforts” throughout the trial to arouse prejudice against the defendant because of his wealth. Id. at 32. The Second Circuit reversed the conviction because it concluded that this conduct by the prosecutor amounted to prejudicial error. In the present case, the prosecutor made two references to money and greed as appellants’ motivation — one during the opening statement and the other during closing argument. These two isolated references do not constitute misconduct and they clearly do not amount to prejudicial error. Appellants claim that the district court committed reversible error by allowing the case agent to be in the courtroom throughout the trial. They assert that the case agent abused his position by relaying information and coaching prospective government witnesses. Appellants have cited nothing in the record to substantiate this allegation. Moreover, we find that the district court did not abuse its discretion in allowing the case agent to remain at the prosecutor’s table. See, e.g., United States v. Alvarado, 647 F.2d 537, 540 (5th Cir.1981). The case agent was exempt from sequestration. See Fed.R.Evid. 615(2) and (3); United States v. Perry, 643 F.2d 38, 53 (2d Cir.), cert. denied sub nom., 454 U.S. 835, 102 S.Ct. 138, 70 L.Ed.2d 115 (1981); United States v. Alvarado, 647 F.2d at 540. Finally, appellants claim that the IRS agents manipulated the taped conversations and were poor witnesses. The trial court judge and jury are in the best position to judge the accuracy of the taped conversations and the credibility of the witnesses. We find no merit in these claims. IV. Challenges to 18 U.S.C. § 371 Appellants raise several challenges to the conspiracy statute under which they were indicted and convicted. We reject each challenge. A. Use of 18 U.S.C. § 371 to Indict for Violation of Tax Law Appellants contend that 18 U.S.C. § 371 was preempted by Congress’ enactment of the comprehensive penal provisions of the Internal Revenue Code. Thus, appellants assert that 18 U.S.C. § 371 was not intended to cover conspiracies to defraud the IRS. Relying on this premise, appellants argue that the indictment under this statute was improper and should have been dismissed. A similar argument was made by the defendant in United States v. Shermetaro, 625 F.2d 104, 109-11 (6th Cir.1980). The Sixth Circuit rejected the argument stating “there is no merit in the contention of appellant that Congress has preempted the field of federal income tax law in Title 26 so as to prevent prosecutions for conspiracy to violate those laws pursuant to 18 U.S.C. § 371,” Id. at Ill. The Sixth Circuit expressly concluded that conspiracies to defraud the IRS are indictable offenses under 18 U.S.C. § 371. We agree with the Sixth Circuit. Appellants’ indictment under 18 U.S.C. § 371 was proper. B. Constitutionality of “Conspiracy to Defraud” Prong of 18 U.S.C. § 371 Appellants also urge us to declare unconstitutionally vague the “conspiracy to defraud the United States” prong of 18 U.S.C. § 371. In support of their contention that the “conspiracy to defraud the United States” prong of § 371 is unconstitutionally vague, appellants rely exclusively on a case decided by the West Virginia Supreme Court, State ex rel. Whitman v. Fox, 160 W.Va. 633, 236 S.E.2d 565 (1977). Appellants’ reliance on Whitman is misplaced. In Whitman, the West Virginia Supreme Court ruled on the constitutionality of its state conspiracy statute, W.Va.Code, 61-10-31 (1978), which was modeled on the federal conspiracy statute, 18 U.S.C. § 371. The court evaluated the state conspiracy statute under the due process clause of the state constitution and found that the section making it unlawful “to defraud the State, the state or any ... county or municipality of the State ...” was unconstitutionally vague. The court held that this prong of the state conspiracy statute “does not adequately inform the citizenry of the activity which may be considered criminal under the statute.” Id. 236 S.E.2d at 569. In so holding, the state court commented that the federal conspiracy statute had “miraculously withstood constitutional scrutiny.” Id. However, the state court emphasized that it did not “disparage the Federal Courts’ wisdom in permitting the word ‘defraud’ in 18 U.S.C. § 371 [1948] to take an expanded meaning with successive imaginative prosecutions.” Id. We are convinced that the conspiracy to defraud prong of 18 U.S.C. § 371, as applied in this case, is not unconstitutionally vague. In United States v. Mazurie, 419 U.S. 544, 95 S.Ct. 710, 42 L.Ed.2d 706 (1975), the Supreme Court stated “[i]t is well established that vagueness challenges to statutes which do not involve First Amendment freedoms must be examined in the light of the facts of the case at hand.” Id. at 550, 95 S.Ct. at 714. Accord United States v. Bohonus, 628 F.2d 1167, 1173-74 (9th Cir.), cert. denied, 447 U.S. 928, 100 S.Ct. 3026, 65 L.Ed.2d 1122 (1980); United States v. Broncheau, 597 F.2d 1260, 1263 (9th Cir.), cert. denied, 444 U.S. 859, 100 S.Ct. 123, 62 L.Ed.2d 80 (1979). In examining a statute for constitutional vagueness, we consider whether a person of average intelligence would reasonably understand that his or her conduct is proscribed. United States v. Bohonus, 628 F.2d at 1174; United States v. Broncheau, 597 F.2d at 1263. Moreover, “[a] vagueness challenge will not be upheld if judicial explication- of a statute provides sufficient clarity to afford- fair notice.” United States v. Bohonus, 628 F.2d at 1174. In Dennis v. United States, 384 U.S. 855, 86 S.Ct. 1840, 16 L.Ed.2d 973 (1966), the Supreme Court emphasized that the conspiracy to defraud prong of 18 U.S.C. § 371 reaches any conspiracy for the purpose of impairing, obstructing or defeating the lawful function of any government agency. Id. at 861, 86 S.Ct. at 1844. Thus, 18 U.S.C. § 371 clearly applies to conspiracies to impede, impair, obstruct, or defeat the lawful function of the Department of Treasury in the collection of income taxes. See, e.g., United States v. Turkish, 623 F.2d 769, 771 (2d Cir.1980), cert. denied, 449 U.S. 1077,101 S.Ct. 856, 66 L.Ed.2d 800 (1981). Appellants had fair notice that their conduct would fall within the proscriptions of 18 U.S.C. § 371. Furthermore, we note that 18 U.S.C. § 371 is, by definition, a specific intent crime. The mens rea requirement of § 371 eliminates any objection that the statute punishes the accused for an offense of which he or she was unaware. See, e.g., United States v. Bohonus, 628 F.2d at 1174. Taking each of these considerations into account, we reject appellants’ vagueness challenge to § 371. Appellants had sufficient notice that conspiracy to obstruct the collection of taxes was punishable under 18 U.S.C. § 371 and that their conduct might well fall within the ambit of this section. C. Embryonic Conspiracy Relying on United States v. Wieschenberg, 604 F.2d 326 (5th Cir.1979), and United States v. Tarnopol, 561 F.2d 466 (3rd Cir.1977), appellants contend that the conversations between themselves and the IRS agents were too “embryonic” in nature to support a conviction for conspiracy to defraud the IRS. Essentially, appellants argue that the evidence was legally insufficient to go to the jury. We reject this claim as did the dist