Once [Russian physicist Igor Tamm] arrived in a neighboring village, at the period when Odessa was occupied by the Reds, and was negotiating with a villager as to how many chickens he could get for a half-dozen silver spoons, when the village was seized by one of the Makhno bands, who were roaming the country harassing the Reds. Seeing his clothes (or what was left of them), the insurgents brought him to the Ataman, a bearded fellow in a tall black for hat with machine-gun cartridge ribbons crossed on his broad chest and a couple of hand grenades in his belt.(Quoted from George Gamow, My World Line, 1970.)
"You son-of-a-bitch, you Communist agitator, undermining our mother Ukraine! The punishment is death."
"But no," answered Tamm. "I am a professor at the University of Odessa and have come here only to get some food."
"Rubbish!" retorted the leader. "What kind of professor are you?"
"I teach mathematics."
"Mathematics?" said the Ataman. "All right! Then give me an estimate of the error one makes by cutting of Maclaurin's series at the nth term. Fail, and you will be shot!"
Tamm could not believe his ears... . With a shaking hand, and under the muzzle of the gun, he managed to work out the solution and handed it to the Ataman.
"Correct!" said the Ataman. "Now I see that you really are a professor. Go home!"