The philosopher Bertrand Russell, with A N Whitehead, published Principia Mathematica, a three-volume work on the foundations of mathematics, in 1910. It is an attempt to derive, absolutely rigorously, all mathematical truths from a well-defined set of axioms and inference rules in symbolic logic.
Volume I, page 379 contains the assertion: "From this proposition it will follow, when arithmetical addition has been defined, that 1+1=2." The proof is actually completed in Volume II, page 86, accompanied by the comment, "The above proposition is occasionally useful."
It is however worth pointing out, from a purely pragmatic and (may I say) pedantic point of view, that the page numbering of the book itself runs consecutively from the first page, which is numbered 1. It does not wait for the operation of integer addition to be fully established first.
