17 karma · joined May 23, 2018
If you study math for some time, you'll realize that people in math community (especially students) like to repeat math related cliches (not necessarily true) over and over again. This is that sort of folk lore.
If I were to guess the whys of not including the solutions, I'd say it is to save space as detailed answers to even half the exercises take up considerable space; also "laziness" because writing detailed, explanatory answers is no different from writing the rest of the book. Who wants to do double the work ? :
[1] https://books.google.com/books?id=PPc_2qUhXrAC&pg=PA1&source...
[2] https://www.amazon.com/Mathematical-Proofs-Transition-Advanc...
[3] https://books.google.com/books?id=n0tuBAAAQBAJ&pg=PA4&source...
[4] https://books.google.com/books?id=J9RLuhDRWGQC&pg=PR6&source...
If you're on a budget, check out the free ones like [1] Book of Proof by Richard Hammack, [2] Math Foundations of Computing by Keith Schwarz
[1] https://www.people.vcu.edu/~rhammack/BookOfProof/
[2] https://web.stanford.edu/class/cs103/notes/Mathematical%20Fo...
[0] https://books.google.com/books?id=E9UlDwAAQBAJ&pg=PA1&source...