US Copyright Office, Compendium of US Copyright Office Practices… (1984)
“ Ideas, methods, systems, or the like are not copyrightable, regardless of the form in which they may be described, explained, or embodied in a work. In no case does copyright protection for an original work of authorship extend to any idea, procedure, process, system, method of operation, concept, principle, or discovery, regardless of the form in which it is described, explained, illustrated, or embodied in such work. ”
