An engineer, a physicist and a mathematician (it is said) were holidaying in Scotland. Glancing from a train window, they observed a black sheep in the middle of a field.
"How interesting," observed the engineer, "the sheep in Scotland are black!"
To which the physicist responded, "No, no! All we know is that at least some Scottish sheep are black!"
The mathematician gazed heavenward in supplication, and then intoned, "In Scotland there exists at least one field, which contains at least one sheep, at least one side of which is black."