Nerd joke

Here's a joke from my coworker Ed:

An infinite number of mathematicians walk into a bar.

One of them approaches the bartender. The bartender asks, "What'll you have?"

"A beer," the mathematician says.

"And for you?" the bartender asks the next mathematician.

"Half a beer."

The bartender pauses, then moves on. "How about you?" he asks the third mathematician.

"A quarter of a beer."

The bartender stops. "You're all idiots," he says. Then he pours two beers and walks away.