A friend told me the story. He is already in his age, accordingly, the story happened in the last century, when he was studying at the institute.

Lectures on Mat. The analysis. Prepod tells something, writes on a board. Then suddenly he dies, and without saying a word, flows out of the audience.

The reason came to light later. It turned out that he was driving with his granddaughter in a tram, taking her to the garden. On the way, he saw his institute and left. And about the granddaughter I remembered only in the middle of the lecture and ran to look for her. She, in turn, did not get confused and went to the right stop. So it all ended safely.