[Mc91]

In my CS major, continuous math, discrete math, graph theory, probability and statistics, linear algebra etc. were prerequisites to other courses. So see if those books are blocked as a "threat to order".

If those get through and he reads through them, try sending things like "An Introduction to Formal Languages and Automata", "A First Course in Combinatorial Optimization" and this sort of thing.

There are also prison reform groups like FAMM that you can talk to.