Not proving solutions to textbooks seems to be a common theme in mathematics and theoretical computer science. It makes it difficult for those outside of the traditional classroom to learn the material. Instead textbook writers seem to have this adversarial approach against readers, thinking they’ll “cheat themselves” if they look up solutions or attempt to verify their work. Experts make mistakes, beginners would presumably make even more mistakes. Without a feedback mechanism beginners can’t truly know whether their logic is impeccable or if they have a subtle error that they themselves cannot detect. They could easily fool themselves that they have correct understanding.
Due to that I will not recommend this current book to any colleagues.
If you want an example of a fellow hacker news member that did things right, check out http://joshua.smcvt.edu/linearalgebra/
He provides solutions and lecture videos... this is truly a democratization approach to learning and a model that other academics should follow.