"Let us suppose that we have set the problem of finding a solution to the equation \scriptstyle x^2=2. \, This is a problem for which the Babylonians around 1700 BC found the excellent approximation \scriptstyle \sqrt{2}. ...This is the identical problem which Pythagoras asserted had no fractional solution and in whose honor he was supposed to have sacrificed a hecatomb of oxen—the problem which caused the existentialist crisis in ancient Greek mathematics. The \scriptstyle \sqrt{2} exists (as the diagonal of the unit square); yet it does not exist (as a fraction)!"