1. The problem statement, all variables and given/known data Problem 63 from Gelfand's book Algebra asks "are the father of the son of NN and the son of the father of NN the same person?" 2. Relevant equations This problem is in a section about the square of a sum formula. (a+b)2 = a2+2ab+b2 3. The attempt at a solution If NN has a biological son x, then x's biological father must be NN. If NN has a biological father y, then y's biological son is not necessarily NN because NN could have brothers. When I first did this problem a couple years ago I wondered how this was relevant at all. Now I interpret this as Gelfand's way of introducing the idea that both a2 and (-a)2 equal a2. Rational exponents are covered already in an earlier section. Can anybody confirm this, or does anyone have a differing interpretation?