add Isomorphism -- Mathematics of Programming (#8670)

books/free-programming-books-subjects.md

@@ -534,6 +534,7 @@ Books that cover a specific programming language can be found in the  [BY PROGRA
 * [A Mathematical Theory of Communication](https://archive.org/details/bstj27-4-623) - Claude E.Shannon
 * [Discrete Structures for Computer Science: Counting, Recursion, and Probability](http://cglab.ca/~michiel/DiscreteStructures/) - Michiel Smid
 * [Exploring Math for Programmers and Data Scientists](https://freecontent.manning.com/free-ebook-exploring-math-for-programmers-and-data-scientists/) - Paul Orland
+* [Isomorphism -- Mathematics of Programming](https://github.com/liuxinyu95/unplugged) - Larry LIU Xinyu
 * [Mathematics for Computer Science](https://courses.csail.mit.edu/6.042/spring18/mcs.pdf) - Eric Lehman, F. Thomson Leighton, Albert R. Meyer (PDF)