 In 1925, Andrei Kolmogorov, at the age of 22, published the first (partial) formalization of intuitionistic logic, and also made an extensive comparison with formalized classical logic, in a paper called “On the principle of the excluded middle”. As van Dalen has suggested (Hesseling 2003: 237), Kolmogorov probably had come into contact with intuitionism through Alexandrov or Urysohn, who were close friends of Brouwer’s. Kolmogorov was in any case remarkably well-informed, citing even papers that had only appeared in the Dutch-language “Verhandelingen” of the Dutch Academy of Sciences (Brouwer 1918B, 1919A, 1921A).