 Clearly, to make a systematic comparison possible, one needs a codification of intuitionistic logic in a formal system. On the intuitionistic view that cannot exist, as logic is as open-ended as the mathematics it depends on. But one may formalize fragments of intuitionistic logic. The relevant papers here are Kolmogorov 1925, Heyting 1928 (unpublished), Glivenko 1928, Glivenko 1929, and Heyting  1930.[16]  But perhaps the first to give systematic thought to the matter was Paul Bernays. In a letter to Heyting of November 5, 1930, he wrote: