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Text: Nor do other aids to interpretation strengthen their case. The practice of treaty signatories counts as evidence of the treaty's proper interpretation, since their conduct generally evinces their understanding of the agreement they signed. See Trans World Airlines, Inc. v. Franklin Mint Corp., 466 U.S. 243, 259 (1984); Factor v. Laubenheimer, 290 U.S. 276, 294-295 (1933). The Government's regular compliance with requests for information by Canadian authorities without inquiring whether they intend to use the information for criminal prosecution therefore weighs in favor of its reading of Articles XIX and XXI. Similarly, "[a]lthough not conclusive, the meaning attributed to treaty provisions by the Government agencies charged with their negotiation and enforcement is entitled to great weight." Sumitomo, 457 U. S., at 184-185. See also Kolovrat v. Oregon, 366 U.S. 187, 194 (1961). The IRS' construction of the 1942 Convention repudiates rather than confirms the interpretation respondents ask us to adopt. Finally, the result urged by respondents would contravene Congress' main reason for laying down an easily administrable test in § 7602(c): "[S]ummons enforcement proceedings should be summary in nature and discovery should be limited." S. Rep. No. 97-494, Vol. 1, p. 285 (1982). If respondents had their way, disputes would inevitably arise over whether a Canadian tax investigation had progressed to a point analogous to a Justice Department referral when Revenue Canada made its request for information, thereby "spawn[ing] protracted litigation without any meaningful results for the taxpayer." Ibid. It seems unlikely that Congress would have welcomed this result when it ratified the 1942 Convention, or that Congress intended it when it approved the bill containing what is presently § 7602(c).