* The proof of Theorem 1.9.3 on page 80 is wrong when it says "But
  this implies that partial(Psi)/partial(x)=0."

  This can't be true because we know that partial(Psi)/partial(x) is
  actually M, and that has no reason to be zero. What it should say is
  "This implies that $d Psi/d x =0." (In other words, they confused
  partial derivative with total derivative). 

  So if both x and y are read as functions of x, then Psi is a
  constant. (The other stuff in the proof starting with "Consequently"
  can and should be erased.)

* In problem 26 on page 160 (part of handgraded assignment #5 for
  lesson 12), it should say Delta_2=a_{1,1}b_2- a_{2,1}b_1, and not
  Delta_2=a_{1,1}b_2- a_{1,2}b_1 

* In #30, p. 353, in the Purdue package version of the book, the
  statement T(3x^2+2)=2(x+3) should be instead T(3x+2)=2(x+3). The
  problem is correct in the non-Purdue 3rd edition of the book.