I THINK the commenter was referring to the Computational Theory or Complexity Theory of which they do indeed have no recommendation (Sipser is the common one).
@galeaspablo, sorry I should have been more clear. What I meant is basically the comment above. I highly recommend "Introduction to the Theory of Computation" by Sipser.
As I mentioned in my original comment, I barley passed Calculus. CS Theory is still math, but just... without numbers. The class felt more like solving puzzles, if anything. Writing proofs and doing homework was fun. I regret renting the book, I'm thinking of buying it just to work on the exercises within.
Thanks for the clarification. I think teachyourselfcs is a great resource, and having gone through some of the books and seen their rigor (references everywhere, theory that has taken millions of hours in dissertations/papers/patents/peer review), I would have taken issue with not labelling the resources as part of the theory in the field. After all I am sure CS coursework generally cares about algorithms, data structures, relational databases, operating systems, discrete mathematics, networking, distributed systems, etc.
