The Johansson/Heyting letters and the birth of minimal logic Tim van der Molen Abstract: In 1935 and 1936 Johansson and Heyting exchanged a series of letters. This exchange inspired Johansson to develop his minimal logic which he ultimately published in an article in 1937. This report summarises Johansson's article and letters, and discusses a number of interesting details of the letters. Keywords: Johansson, Heyting, minimal logic, implication, ex falso quodlibet