license information missing?

I can not find a license information for the book (neither in Al's homeage nor in the github project).
I assume that it is some kind of creative-commons license (hopefully cc-by-sa?)
Please, if possible, add that information explicit.

The issue points to the book, Al's homepage, and the GitHub project, but names no repository file. First check those locations for existing license information and ask the maintainer to confirm the intended license; done means the chosen license is stated explicitly in the project and book materials.

Written by the indexing model from the issue text.