diff --git a/books/free-programming-books-subjects.md b/books/free-programming-books-subjects.md
index 70f359e4c..059b0b6bf 100644
--- a/books/free-programming-books-subjects.md
+++ b/books/free-programming-books-subjects.md
@@ -144,7 +144,7 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 * [Clever Algorithms Nature-Inspired Programming Recipes](https://bjpcjp.github.io/pdfs/ruby/Clever-Algorithms.pdf) - Jason Brownlee (PDF) (CC BY-NC-SA)
 * [Getting Started with Artificial Intelligence , 2nd Edition](https://www.ibm.com/downloads/cas/OJ6WX73V) - Tom Markiewicz, Josh Zheng (PDF)
 * [Graph Representational Learning Book](https://www.cs.mcgill.ca/~wlh/grl_book/) - William L. Hamilton
-* [Introduction to Autonomous Robots](https://github.com/correll/Introduction-to-Autonomous-Robots/releases) - Nikolaus Correll (PDF)
+* [Introduction to Autonomous Robots](https://github.com/correll/Introduction-to-Autonomous-Robots/releases) - Nikolaus Correll (PDF) (CC BY-NC-ND)
 * [Machine Learning For Dummies®, IBM Limited Edition](https://www.ibm.com/downloads/cas/GB8ZMQZ3) - Daniel Kirsch, Judith Hurwitz (PDF)
 * [On the Path to AI: Law’s prophecies and the conceptual foundations of the machine learning age](https://link.springer.com/book/10.1007/978-3-030-43582-0) - Thomas D. Grant, Damon J. Wischik (PDF, EPUB)
 * [Paradigms of Artificial Intelligence Programming: Case Studies in Common Lisp](https://github.com/norvig/paip-lisp) - Peter Norvig