Actually it is, at the end of the first section https://mapio.github.io/programming-with-escher/#Programming-with-Escher https://mapio.github.io/programming-wit

Actually it is, at the end of the first section https://mapio.github.io/programming-with-escher/#Programming-with-Escher https://mapio.github.io/programming-with-escher/#Programming... the sentence reads: "The source notebook is available on GitHub (under GPL v3), feel free to use issues to point out errors, or to fork it to suggest edits. Square Limit and tiles."