[Jonster]

Full = empty is pretty easy.

You got a pint glass, that's half full, so it's half empty too, so it can be said that:
1/2 full = 1/2 empty
Multiply both sides by 2, and you get
full = empty

crap innit
(by the way, it's not true because full and empty aren't maths terms, so doesn't count)

Sorry to go majorly off topic too