## Nikolai Luzin (1883 - 1950)

It seems the set of natural numbers is not an absolutely objective formation. It seems it is a function of the mind of the mathematician who happens to be speaking of a set of natural numbers at a given moment. It seems there are, among the problems of arithmetic, those that absolutely cannot be solved.

Quoted in M Gessen, *Perfect rigour* (New York 2009)