Topologist

A student was doing miserably on his oral final exam in General Toplogy. Exasperated by the student's abysmal performance up to that point, the professor asked the student "So, what _do_ you know about topology?"

The student replied, "I know the definition of a topologist."

The professor asked him to state the definition, expecting to get the old saw about someone who can't tell the difference between a coffee cup and a doughnut.

Instead, the student replied: "A topologist is someone who can't tell the difference between his ass and a hole in the ground, but who can tell the difference between his ass and _two_ holes in the ground."

The student passed.

-- David Gonda