Dawid writes, "long live humor". How does he show in his diary that he had a sense of humor?

In page 33, in the Diary of Sierakowiak, there were entries like "And the railway station in Zbaszyn has been taken back from the Germans! We disperse full of joy and go to sleep" and "Long live humor; down with hysteria." And in page 21, we find that he had a good time with his friends in a summer camp. Quotes like these show that he wanted to come out of the gloom at least for a while and cherish those in his mind.