There was a lecture on mathanalysis. The teacher diligently proved the next smart theorem, the students recorded it, and the two girls at the last party discussed how they spent yesterday night. The teacher reached the end of the proof, put a fat point and, turning to the students, said loudly:

What I needed to prove!

When the teacher turns, everyone in the audience is silent, so was it this time. In the sudden silence, a voice full of sincere surprise is heard of one of the girls, who was so engaged in the conversation that she did not have time to react:

It cannot be!

The teacher, after these words, stunned, once again looked closely at his recordings and said with a confident voice:

You can see for yourself, it’s all right.

The girl's response drowned in a friendly whistle, so history did not save him.