... (copyright does not cover the implementation).
Wrong. Copyright does cover implementation. That's the only thing it covers. Or are you unaware that software is under copyright protection?
Content quoted from http://copyright.gov/help/faq/...
What does copyright protect?
Copyright, a form of intellectual property law, protects original works of authorship including literary, dramatic, musical, and artistic works, such as poetry, novels, movies, songs, computer software, and architecture. Copyright does not protect facts, ideas, systems, or methods of operation, although it may protect the way these things are expressed. See Circular 1, Copyright Basics, section "What Works Are Protected."