One plus one

The formula that appears on the homepage is a mathematical proposition, more commonly known as 1+1=2 in the special case of integer arithmetic. The unusual notation is from “Principia Mathematica” and so are the following excerpts.



Proof that 1 + 1 = 2. An “occasionally useful proposition”.


The proof is taken from Principia Mathematica. It appears in the second volume, after all the necessary mathematical machinery has been set up.


An announcement of the proof appears in the first volume.