In Aquilino v. United States, 363 U.S. 509, 513, 80 S.Ct. 1277, 4 L.Ed.2d 1365 (1960) the Court said: The threshold question in this case, as in all cases where the Federal Government asserts its tax lien, is whether and to what extent the taxpayer had "property" or "rights to property" to which the tax lien could attach. In answering that question, both federal and state courts must look to state law, for it has long been the rule that "in the application of a federal revenue act, state law controls in determining the nature of the legal interest which the taxpayer had in the property . . . sought to be reached by the statute. (363 U.S. at 512-513, 80 S.Ct. at 1280.)