I'd like to use code from project A that was licensed under GPL-3.0-or-later in project B, which is also going to be licensed under GPL-3.0-or-later. What should the license headers in the source files look like?
I found a detailed description of how to cite permissively licensed code here: https://softwarefreedom.org/resources/2007/gpl-non-gpl-collaboration.html. The suggestion is to include the following phrase in the header:
This file incorporates work covered by the following copyright and permission notice:
This seems like overkill if I'm using GPL-licensed code in a GPL-licensed project (I'd have to put the GPL-3.0-or-later license header into each source file twice). Is there a better way to do it, or should I still follow this pattern? What should the license header look like?