Last night I dreamed that the person whom so far I was knowing as a cleaner in the department was actually a professor! Today, when I saw him cleaning, I was not sure that I was not dreaming.

Inside the campus, given a person P, the problem of detecting whether he is a professor or a student is in NP. Therefore, a few heuristics are proposed by our research community (especially those who initially failed to detect a professor):

• if P is talking loudly to someone outside the class, P is a student (a professor is nearby and the student is trying to show his knowledge).
• if you have never seen P and in the corridor, you meet P coming from the opposite side, and if P stares at you for more than 3.142/4.0 second, he is a professor (expecting a greeting from you idiot, say “Hello.”).
• if P stays till the end of a student farewell function, he is not a professor.
• on arrival to a coffee-board, if P looks around at the public before going to the food counter, he is not a professor.
• if it is given that in a discussion group at least one professor exists, the person who has the maximum expanse of the vertical motion of his head, is a professor.

Corollary: If you encounter a false positive (detecting P to be a professor when actually he is not), it is fine. However, false negatives (detecting P to be a student when actually he is a professor) can prove costly.