[hnthwaccount]

This is amazing for self-learners. Free textbook, free lecture videos, free solutions. I bought a hard copy of this book when I first came across this resource.

This is really outstanding because most textbooks do not contain full solutions and it can be difficult for self-learners without access to universities, tutors, peers to debug errors or check their work. If such a student ever got stuck, then it could be hard to move forward. One solution is to use sites like Math Stack Exchange, but I can imagine it would be tedious to do multiple proofs every chapter and type every single one of them up for someone to check. Some would argue that if your solution is correct then you should be able to rigorously justify each step and you should “know” in the end of its right. Beginners often don’t have the mathematical maturity developed to do this yet and even experts make mistakes in their proofs.

If you had a question, then I could see scenarios where the question would be closed on sites like MSE for being duplicates or some odd thing that didn’t satisfy some sort of rule somewhere. These are more barriers for the self-learners that those in classrooms don’t necessary face and textbooks are typically written for those that access to professors.

I think more math textbooks should be written this way.

[radmuzom]

I logged into post the same comment - instead up-voted yours.

While online courses are often good, I hate the idea of learning math by answering multiple choice questions. The fact that this provides the complete proofs as answers will help one to check their own thought process (assuming they don't cheat and look at the solution without putting in any effort).