Re: Clarification on the GNU Free Documentation License (GFDL) Applicability

[Valentin Petzel]

Hello Peter,

> ### My Concerns
> 
> 1. **Scope of Source Code Disclosure**:
>    - According to the GFDL, if I use LilyPond and LaTeX to write a book and
> sell it on Amazon, am I required to disclose the entire LaTeX source code
> of the book, or just the parts that include LilyPond code? For instance, if
> the book contains dozens or even hundreds of musical excerpts, do I need to
> disclose all the LaTeX code or just the musical notations?

No. The GFDL is the license telling you what you may or may not do with the 
Lilypond documentation. It does not accect all books created using Lilypond. 
Now, if in your book you were to include significant parts of the documentation 
the license will apply. The lilypond language itself is not protected in any 
real way afaik, and afaik it would even be legally hard to try to do so. There 
have been discussions as to whether Lilypond scores qualify as software and 
thus the GPL applies. But general consensus is that this is bogus, and that a 
PDF is not a software.

So long stories short, you do not have to disclose anything (unless you are 
actually incorporating the docs or anything).

> 2. **Applicability of GFDL**:
>    - Does the GFDL apply only to the documentation of LilyPond, or does it
> also cover the software itself? This distinction is crucial for my decision
> to use LilyPond for writing and publishing books.

It only applies to the documentation. Lilypond is licensed under the GPL 
(which does not cover documentations, hence the need).

> 3. **Use of Fonts**:
>    - If I use the default fonts provided by LilyPond 2.24.4 to generate PDF
> files, does this imply that I need to comply with the GPL license as well?
> Would this require me to disclose the source code?

GPL does not cover fonts. The fonts (and only the musical fonts do actually 
come from Lilypond) are licensed as under the SIL OFL. Which means you are 
free to do whatever you want with documents set in these fonts.

> 4. **Feasibility of Commercialization**:
>    - If I must disclose the source code while selling the books, others can
> easily recompile the source to generate the PDF, eliminating the need to
> purchase the book. In this case, does it still make sense to use LilyPond
> for writing and selling books?

Does not apply, as it builds on false premisses. But let’s assume this was the 
case — clearly even you do not have the sources, you can copy pdfs and scan 
physical media. So this is not really changes by having the source code. Now, 
if this was really GPL like the key thing would actually be you having to 
distribute under the same license, giving other the right to redistribute it. 
But as already said, this does not apply here in the first case.

Some closing words: I’m quite sure that all people in Lilypond community would 
welcome seeing more usuage of Lilypond, also in professional and commercial 
settings. Because we care about Lilypond. It is always good to have people 
using the software and achieving things with it. Because Lilypond only works 
because it has people using it.

Cheers,
Valentin

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