diff --git a/books/free-programming-books-langs.md b/books/free-programming-books-langs.md
index b47ef38e5..cf1c4e3d6 100644
--- a/books/free-programming-books-langs.md
+++ b/books/free-programming-books-langs.md
@@ -2001,7 +2001,7 @@ Books on general-purpose programming that don't focus on a specific language are
 * [Hitchhiker's Guide to Python!](http://docs.python-guide.org/en/latest/) (2.6)
 * [How to Code in Python 3](https://assets.digitalocean.com/books/python/how-to-code-in-python.pdf) - Lisa Tagliaferri (PDF)
 * [How to Think Like a Computer Scientist: Learning with Python, Interactive Edition](https://runestone.academy/runestone/books/published/thinkcspy/index.html) - Brad Miller, David Ranum, Jeffrey Elkner, Peter Wentworth, Allen B. Downey, Chris Meyers, Dario Mitchell (3.2)
-    * [How to Think Like a Computer Scientist: Learning with Python 1st Edition](https://greenteapress.com/wp/learning-with-python/) - Allen B. Downey, Jeff Elkner, Chris Meyers (2.4) (HTML, PDF)
+    * [How to Think Like a Computer Scientist: Learning with Python 1st Edition](https://greenteapress.com/wp/learning-with-python/) - Allen B. Downey, Jeff Elkner, Chris Meyers (2.4) (HTML, PDF) (GFDL)
     * [How to Think Like a Computer Scientist: Learning with Python 2nd Edition](https://openbookproject.net/thinkcs/python/english2e/) - Jeffrey Elkner, Allen B. Downey, Chris Meyers (Using Python 2.x)
     * [How to Think Like a Computer Scientist: Learning with Python 3 (AoPS Edition)](https://artofproblemsolving.com/assets/pythonbook/) - AoPS Incorporated, Peter Wentworth, Jeffrey Elkner, Allen B. Downey, Chris Meyers (HTML)
     * [How to Think Like a Computer Scientist: Learning with Python 3 (RLE)](https://openbookproject.net/thinkcs/python/english3e/) - Peter Wentworth, Jeffrey Elkner, Allen B. Downey, Chris Meyers [(PDF)](https://www.ict.ru.ac.za/Resources/cspw/thinkcspy3/thinkcspy3.pdf)
@@ -2025,7 +2025,7 @@ Books on general-purpose programming that don't focus on a specific language are
 * [Lectures on scientific computing with python](https://github.com/jrjohansson/scientific-python-lectures) - J.R. Johansson (2.7)
 * [Making Games with Python & Pygame](https://inventwithpython.com/pygame/chapters/) - Al Sweigart (3.2) (CC BY-NC-SA)
 * [Math for programmers (using python)](https://akuli.github.io/math-tutorial/)
-* [Modeling and Simulation in Python](https://greenteapress.com/wp/modsimpy/) - Allen B. Downey (PDF)
+* [Modeling and Simulation in Python](https://greenteapress.com/wp/modsimpy/) - Allen B. Downey (PDF) (CC BY-NC)
 * [Modeling Creativity: Case Studies in Python](https://arxiv.org/pdf/1410.0281.pdf) - Tom D. De Smedt (PDF)
 * [Natural Language Processing (NLP) with Python — Tutorial](https://medium.com/towards-artificial-intelligence/natural-language-processing-nlp-with-python-tutorial-for-beginners-1f54e610a1a0) (PDF)
 * [Natural Language Processing with Python](http://www.nltk.org/book/) (3.x)