review the tax court’s factual findings for clear error, its legal conclusions de novo, and its application of the law to the facts for clear error. Kikalos v. Comm’r, 434 F.3d 977, 981-82 (7th Cir.2006); Yasha v. Comm’r, 861 F.2d 494, 499 (7th Cir.1988) (“The question whether a particular transaction has economic substance, like other questions concerning the application of a legal standard to transactions or events, is governed by the clearly erroneous standard”). Section 6901 of the Internal Revenue Code authorizes the IRS to proceed against the transferees of delinquent taxpayers to collect unpaid tax debts. But the statute provides only a procedural device for proceeding against a taxpayer’s transferee. See Comm’r v. Stern, 357 U.S. 39, 42-43, 78 S.Ct. 1047, 2 L.Ed.2d 1126 (1958) (<HOLDING>). Substantive liability is governed by state
holding that the predecessor to  6901 is purely a procedural statute recognizing the existence of purely jurisdictional elements holding that under alabama law the law of the forum applies to procedural matters and that in most instances the statute of limitations is considered to be a procedural rule holding fees mandatory under predecessor statute of  38001 holding in the context of the predecessor statute to  922g that the interstate commerce element is met by demonstrating a minimal nexus