please tell me the most obscure joke you know

(feel free to explain or not explain it, depending on what you find more amusing to think of me reading it)

@whitequark Q: What's an anagram of Banach-Tarsky?

A: Banach-Tarsky Banach-Tarsky.

@ljrk @whitequark The. B in Benoit B. Mandelbrot stands for Benoit B. Mandelbrot