diff --git a/books/free-programming-books-subjects.md b/books/free-programming-books-subjects.md
index 9c2d76551..cb7902583 100644
--- a/books/free-programming-books-subjects.md
+++ b/books/free-programming-books-subjects.md
@@ -503,6 +503,7 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 * [Foundations of Constructive Probability Theory](https://arxiv.org/pdf/1906.01803.pdf) - Yuen-Kwok Chan (PDF)
 * [Geometry with an Introduction to Cosmic Topology](https://mphitchman.com) - Michael P. Hitchman
 * [Graph Theory](http://compalg.inf.elte.hu/~tony/Oktatas/TDK/FINAL/)
+* [Guide to Discrete Mathematics](https://core.ac.uk/download/pdf/326762636.pdf) - David Gries, Fred B. Schneider (PDF)
 * [How We Got from There to Here: A Story of Real Analysis](https://milneopentextbooks.org/how-we-got-from-there-to-here-a-story-of-real-analysis/) - Robert Rogers, Eugene Boman
 * [Introduction to Modern Statistics](https://openintro-ims.netlify.app) - Mine Çetinkaya-Rundel, Johanna Hardin (HTML, PDF) (email address required for PDF)
 * [Introduction to Probability](https://math.dartmouth.edu/~prob/prob/prob.pdf) - Charles M. Grinstead, J. Laurie Snell (PDF)