[math-fun] Square thirds

Surely everyone other than me already knows this, but when my 7-year-old son asked me this over dinner tonight, I couldn't give him a satisfying answer. Is it possible to dissect a square into 3 congruent pieces in any way other than the trivial one? Surely the answer is no, but I can't think of a proof. --Michael Kleber -- It is very dark and after 2000. If you continue you are likely to be eaten by a bleen.