“Even “1+1=2” is less obvious than it seems at first. Beginning in the early part of the 20th century, mathematicians and philosophers, led at first by Bertrand Russell and Gottlob Frege and later by Ludwig Wittgenstein, Kurt Gödel, Alan Turing, and others, tried to see whether mathematical knowledge–facts like “1+1=2″–could be reduced to the laws of logic.”