Comment Give them license to modify the code (Score 3, Insightful) 447
First of all, client expects to be able to use and MODIFY code you've done for them, both physically and legally. Who owns the code - is the second question. They don't want to own your library - they just want THE LICENSE allowing them to see, modify and use that modified code. It is the same thing as open source, except that they don't get the right to redistribute your library.
Don't be a dick, just give them that license.