diff --git a/books/free-programming-books-subjects.md b/books/free-programming-books-subjects.md
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--- a/books/free-programming-books-subjects.md
+++ b/books/free-programming-books-subjects.md
@@ -183,7 +183,7 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 
 ### Cellular Automata
 
-* [A New Kind of Science](https://www.wolframscience.com/nksonline/toc.html) - Stephen Wolfram
+* [A New Kind of Science](https://www.wolframscience.com/nksonline/toc.html) - Stephen Wolfram (HTML)
 * [An Introduction to Cellular Automata](https://ia801004.us.archive.org/26/items/viviencellularautomata/vivien%20cellular%20automata.pdf) - Hélène Vivien (PDF)
 * [Cellular Automata Machines](https://people.csail.mit.edu/nhm/cam-book.pdf) - Norman Margolus, Tommaso Toffoli (PDF)
 * [Introduction to the Modeling and Analysis of Complex Systems](https://milneopentextbooks.org/introduction-to-the-modeling-and-analysis-of-complex-systems/) - Hiroki Sayama (PDF) (CC BY-NC-SA)