Here is a (slightly shortened) joke from the book The Curious Incident of The Dog in the Night-Time:

There are three men on a train. One of them is an economist and one of them is a logician and one of them is a mathematician.  And they have just crossed the border into Scotland and they see a brown cow standing in a field from the window of the train.

And the economist says, "Look, the cows in Scotland are brown."

And the logician says, "No. there are cows in Scotland of which one at least is brown."

And the mathematician says, "No. there is at least one cow in Scotland, of which one side appears to be brown."