Advice needed for licensing in modus-themes

[Dhavan V <quark@codingquark.com>]

Hello!

I maintain modus-themes[1] for Emacs team. In the process of upgrading
to upstream version, I have come across
license-problem-gfdl-invariants[2] in ~doc/modus-themes.info~ [3].

I do not understand legality of the matter fully and seek advice as to
how this can be easily handled. I am also including Protesilaos
(upstream) to have a conversation with everyone included.

I think it will be of great help if debian-legal could explain the case
and possible solutions to Emacs team as well as upstream.

Thanks!

[1]: https://salsa.debian.org/emacsen-team/modus-themes
[2]: https://wiki.debian.org/qa.debian.org/gfdlinvariant