 Brouwer’s writings are referred to according to the scheme in the bibliography van Dalen 1997a; Gödel’s, according to the bibliography in Gödel 1986, Gödel 1990, Gödel 1995 (except for Gödel 1970); Heyting’s, according to the bibliography Troelstra et al. 1981 (except for Heyting 1928).