A philosophical professor gave a test for students.
The professor put a chair on the table and asked "Using everything we have learned to prove that this chair is not exists".

Students try to write all the best. some students wrote more than 30 pages in an hour to deny the existence of the chair. Only one member of the class stood up and finished the test in less than a minute.

A few weeks later, the point was announced. Most students disappointed because no one reaches point A, except the guy out of the examination room.

All students flocked to him to ask what he was written on the test. He replied:
- I just wrote only a sentence: WHICH IS THE CHAIR ?