During the tea break , John and William were chatting:

John: William, I've been taking night courses for 5 months now and I have an exam next week.

William: oh!

John: For example, do you know who is Graham Bell?

William: No

John: He's the inventor of the phone in 1876; if you take night courses you would know this.

The next day, the same discussion took place:

John: Do you know who is Alexander Dumas?

William: No

John: He's the author of 'The 3 Musketeers', if you take night courses, you would know this.

The next day, once again:

John: And do you know who is Jean Jacques Rousseau?

William: No

John: He's the author of 'Confessions', if you take night courses, you would know this.

This time, William got irritated and said: 'And you, do you know who is George Hunt?'

John: No

William: He's the guy enjoying your wife!! If you stop night courses, you would know this...