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.