ABSTRACT
Daniel sent a letter in reply: “Euler , I’m so glad to hear that you have made a good recovery from that infection! A few days after I received your letter, I walked out to Riehen to talk with your parents. I guess I’m not surprised that you hadn’t written to them about your illness, and I was glad that I was able to tell them about the infection only when I also had the news that you have recovered. I would have hated to leave them wondering and worrying. You know, your parents and I are greatly relieved that you survived that infection, but in fact the world of mathematics should also express relief. If something happens to you, where would we all be? You alone are essential to the progress of mathematics! I hope something like this never happens again.”
