This is a p.s to the mathch-play discussion, in asserting that if you
read something in a textbook, even a closely edited one it must be
correct. I have personally found many mistakes in math and finance
texts this is not that unusual.
It is much more important to have a solid grap of the subject you are
talking about than to rely on verbatim memorization of texts, or to
assert the validity of an argument based on a faulty text over
reasoning.