 Kraïtchik was "agrégé" of the Free University of Brussels, engineer at the Société Financière de Transports et d'Entreprises Industrielles (Sofina), and director of the Institut des Hautes Etudes de Belgique.He died in Brussels.Kraïtchik is famous for having inspired the two envelopes problem in 1953, with the following puzzle in "La mathématique des jeux"