Amy gave me a sly look and then winked at the bartender. In a proud voice she said, “I’m getting a modified Bessel function.”

“A modified Bessel function? I’ve never even heard of that. What is it?”

“It’s related to Bessel functions.”

I had a vague recollection of some sort of Bessel functions from a quantum mechanics course I’d struggled through years ago.

“Oh, that sounds complicated. I don’t think this place is right for me, Amy. I’d better go.” I eased myself off my bar stool and started to put my coat on.

Amy grabbed my arm. “Wait, wait. Don’t go. It took me years to work up to Bessel functions. There are lots of easier things you can try. Trust me. It will be fun.”

That felt reassuring but then she started getting excited again.

“Take any integral you like. They’ve got practically all of them. Improper, double, triple. There are classics like Lebesgue or Stieltjes. Feeling frisky? Try a divergent one.”

While I was thinking it over, a man in a three-piece suit, obviously tipsy from too much mathematics, stumbled up to the bar and shouted, “I want a Cauchy principal value!”