 1909–1913 In a very productive four years, Brouwer founds modern topology, as a chapter of classical mathematics. Highlights: invariance of dimension, fixed point theorem, mapping degree, definition of dimension. As van Dalen (2005, p. 450) observes, Brouwer’s definition of dimension seems to be the first reformulation of an inductive definition as a game. A pause in his intuitionistic program.