I have a header and source file which the majority is mine, however there is at least one function which uses a few lines of code from another library (Apache 2.0) I will license said files with the same license. What about copyright? There are parts of code which are fully mine which I would like to retain a copyright to. These cannot be (easily) separated. How should put the license to specify that parts of the code are mine?
I know that I need to retain the original copyright.