There are three umpires at a baseball game. One is an engineer, one is a physicist and one is a mathematician. There is a close play at home plate and all three umpires call the man out. The manager runs out of the dugout and asks each umpire why the man was called out.
The physicist says, "He's out because I calls 'em as I sees 'em."
The engineer says, "He's out because I calls 'em as they are."
The mathematician says, "He's out because I called him out."