Math Conundrums

Hey guys 'n' gals,

Just wondering:

DO YOU KNOW ANY FAMOUS MATH CONUNDRUMS THAT HAVE TO DO WITH CALCULUS? IT DOESN'T HAVE TO BE FAMOUS! DO NOT MAKE IT UP!

You see, I need one conundrum for the story that I am writing. If you do know of a conundrum that fits the description above, and one with complicated symbols that no one (but you) will get, please post it in comments. Also, when you do post it, please explain the conundrum, 'cause I need to get it thoroughly.

I was googling conundrums for ages, and I didn't come up with any awesome websites that supplied conundrums. Well, one that supplied formulas, and that was the best I found.

BY THE WAY, IT CAN BE A FORMULA TOO! JUST EXPLAIN IT!

thx

pooja