Gentzen was a very modest, aloof, one could almost say unworldly man, who lived only for his science and only allowed himself to take his mind off it with difficulty. For my wife's sake he accepted under pressure an invitation to a concert, which we caught on too late must have been an ordeal for him. He explained to us after the concert that for him music was a most extremely unpleasant noise. In the last weeks in Prague Gentzen visited us more frequently. The talks at the time naturally turned to when and how we would leave Prague. On 3 May 1945 he appeared with two bottles of wine, the remnant of a package received from his uncle. On 5 May the Czechs began their revolution. I experienced this beginning in a lecture by Gentzen on "Introduction to formal Logic". He accompanied me as far as the tram and took his leave with greetings to my wife and the advice not to speak on the way. On 6th and 7th we spoke by telephone and on 8th of May we were locked up by the Czechs.
On 30 May 1944 Professor Rohrbach introduced me to the lecturer Gentzen. ... His black hair was always parted neatly; he was always very well shaved and his clothing carefully looked after. His fine structured form with the lively black eyes revealed an in no way naive but predominantly intellectually stamped personality. In spite of the gulf between his towering intellectual power and a nobody like me, Gentzen was always a warm and ready-to-help superior. In the evenings and Sundays everyone went his own way. Gentzen spoke however of his dissertation, for which a proper judge could only be found with difficulty ... Gentzen used this calculus frequently for logical clarification - also for banal questions, whether he should go to the cinema. Thereby on notes he wrote tautologies, etc. The secretary probably observed this ... Gentzen showed me a lovely invitation to deliver a lecture to the Institute for Advanced Studies in Princeton. The outbreak of the war hindered all lectures.