> Copyright: all the source code is rewritten so there is no copyright there. ...there is no copyright infringement. You own copyright on the things you create

> Copyright: all the source code is rewritten so there is no copyright there. ...there is no copyright infringement. You own copyright on the things you create (or your employer does when hired by them to do such work.) You infringe others' copyright by using their work in a way that they didn't approve (or goes against how the law says you can use their work.) By creating your own implementation of $THING, you now hold copyright in your implementation. This does not alleviate the patent and trademark concerns.