A friend once told me that he just returned from a defense of a doctoral dissertation at the Department of Mathematics, Belgrade University, where he witnessed an incident he considered quite humorous. My friend knew the young man who defended his thesis, and he went there to lend him some support. Everybody was quiet in the room: the doctoral candidate, the audience—composed of a couple of friends and relatives—huddled together in the back, and the three professors, who were making the last minute preparations and whispering occasionally to each other. And then the doctor-to-be started stomping the floor underneath his desk with his feet—at first slowly and quietly, and later on with vigor and enthusiasm. The rhythmical thud filled the room. The three professors raised their heads. They watched him for a few seconds. One of them said: “Yes?” The room was quiet again. “Cavalry,” the young man replied. After a brief hesitation, the whole room burst into laughter. The professor who asked the question and the doctoral candidate stared at each other a while longer, but ultimately joined the others. By the way, the friend who told me about this was killed in a bus accident some ten years hence. He was en route from Belgrade to Novi Sad, where he taught calculus in a vocational school for machine operators. His bus collided with a train.