There are TWO kinds of federal law (US COde), those USC Titles that were enacted into POSITIVE LAW, and those that WEREN'T. On a State level, it's a difference between actual laws, and mere statutes. And those US Code titles that were NOT enacted into positive law, can be REBUTTED.

Here's a quote:
"Positive law titles of the United States Code, indicated by an asterisk, are legal evidence of the law and need no further authoritative citation as prior acts concerning those titles have been repealed. Other titles to the U.S. Code are "prima facie" evidence of the law (1 USC §204), and are presumed to be the law, but are rebuttable by production of prior unrepealed acts of Congress at variance with the Code. "

For example, USC Title 8 which contains the Immigration and Naturalization Act, is NOT positive law, so it can be rebutted by presenting older federal statutes that contradict it.And one good example of this is the case of US v Braun, where several people were charged for violating federal law for demonstrating near abortion clinic. Most of them lawyered up and lost but one of them went Pro se and introduced evidence which contradicted the federal law that was saying that certain area around that clinic is considered federal land.

What was that evidence? It was Congress' report from 1950's which described exactly what areas are under State jurisdiction, which contradicted the federal law which said that certain area around an abortion clinic is subject to federal law.And the guy who put that Congress's report into his case, WON the case and the judge had to drop all the charges.
This shows you how to beat federal charges when you're accused of violating US Code that hasn't been enacted into positive law. Such as the Title 26 that deals with income tax.

Here's a link to the list of all positive law US Code titles:
http://www.llsdc.org/asse…/sourcebook/usc-pos-law-titles.pdfBTW, this also demonstrates that "prima facie" evidence of the law CAN BE REBUTTED. Such as a ZIP code address being a prima facie evidence of State RESIDENCY.