A short story about students

The lecture on quantum physics has only just begun. Classroom noise disclosed notebooks. Who else runs all in a lather, quiet negotiations ... All right, as usual, after five minutes of the call. However, our Professor X has managed to scribble on the blackboard very long formula. All engaged in rewriting and suddenly the silence was formed. And in this silence suddenly sounded loudly indignant voice:

 - Cho, fool, write !? - Is one student said to the other, looking to book in.

 - No, like all well - thoughtfully replied the professor, moving a few steps away from the board and critically examining the formula ...