While I was at University in England (and I return in 6 weeks)
I was unfortunate to complete (?!) a course called Formal
Construction of Programs which dealt with proving computer
programs fundamentally correct by using pre and post
conditions. The joke below is taken from the book
PROGRAM CONSTRUCTION AND VERIFICATION by Roland C Blackhouse
and is, I assume included in the book to make the subject
matter a little more interesting.
The Logician, the mathematician, the physicist, and the engineer.
'Look at the mathematician', said the logician. 'He observes that
the first ninety-nine numbers are less than a hundred and infers
hence, by what he calls induction, that all numbers are less than a
hundred.'
'A physicist believes', said the mathematician, 'that 60 is
divisable by all numbers. He observes that 60 is divisable by 1,2,3,
4,5, and 6. He examines a few more cases, as 10,20, and 30, taken
at random as he says. Since 60 is divisable also by these, he
considers the experimental evidence sufficent.'
'Yes, but look at the engineer', said the physicist. "An
engineer suspected that all odd numbers are prime numbers. At
any rate, 1 can be considered as a prime number, he argued.
Then comes 3,5, and 7, all indubitably primes. Then there comes
9; an awkward case, it does not seem to be a prime number. Yet 11
and 13 are certainly primes. 'Coming back to 9', he said, 'I
conclude that 9 must be an experimental error'.
Any engineers out there ?