Alfred North Whitehead and Bertrand Russell published *Principia Mathematica* in three volumes from 1910 to 1913. The project attempted to derive all mathematical truths from a set of axioms using symbolic logic. The proof that 1+1=2 doesn't appear until Volume II, around page 362. Russell later said the work took them ten years of grinding labor and nearly broke both of them intellectually.

This is a completely different book from Isaac Newton's *Philosophiae Naturalis Principia Mathematica* (1687), which laid out the laws of motion and universal gravitation. They share a name and nothing else. Newton's is physics; Whitehead and Russell's is pure logic.