Ask HN: Any good math jokes?

I'm trying to come up with a good math joke for our math team t-shirts. Last year we had "Know you limits, don't drink and derive." The shirt included a fuzzy graph.

I'm thinking about using an xkcd comic if the author gives me permission, but the images are somewhat small for t-shirts, so I might have to throw my own together anyways.

Got any good ideas?

Why was 6 afraid of 7?

Because 7 8 9!

(7 ate 9)

An engineer, a physicist, and a mathematician go to a conference together, and split a room in the hotel. They check in and go to sleep. The hotel is old (they couldn't afford anything better on professors' salaries), so the room is heated by a fireplace. A spark jumps out of the fire and catches the rug on fire. The engineer smells the smoke and wakes up. He jumps out of bed, sees the fire, and looks around. The first thing he sees is the ice bucket, so he takes it, fills it up from the sink, and throws the water on the fire. He drops the ice bucket next to the fireplace and goes back to bed.

The fire throws another spark, creating another fire. The physicist wakes up and sees the fire. He calculates that, given the size of the fire, and amount of oxygen needed to be displaced to put out a fire of said size, a glass of water will be sufficient. He fills up his water glass from the sink, and while running to the fire, throws the water at the fire at the exact distance from the fire that gets the water to the fire earliest, putting it out. He drops the glass next to the fireplace and goes to sleep.

The fire sparks once more, and the mathematician wakes up and sees the fire. He looks at the ice bucket and glass sitting next to the fireplace, says "Aha! A solution exists!", and goes back to bed.

It's a math joke, but not one suitable for t-shirts.

friend had a shirt that said

"be there or c squared minus a squared"

lol

There's always the classic, 'Snakes ⊂ ℝ²'.