A mathematician, a chemist, an engineer and a computer scientist are asked to show that all odd numbers are prime.

The mathematician says "3's prime; 5's prime; 7's prime. Therefore, by induction, all odd numbers are prime."

The chemist says "3's prime; 5's prime; 7's prime; 11's prime. 9's not prime — ah well, experimental error. Therefore, all odd numbers are prime."

The engineer just says "3's prime; 5's prime; 7's prime; 9's prime; 11's prime; ..."

And the computer scientist writes a program that prints "1's prime; 1's prime; 1's prime; ..."