What kind of derivative?... (18.20)
Taylor: I just decided to work on a derivative.
Douglas Mason: What kind of derivative?
Taylor: An homage to Vadim Linetsky.
Douglas Mason: Oh. You're in a 'path integral methods' sort of mood, are you?
Taylor: Would you like to help me?
Douglas Mason: You bet.
Vadim Linetsky is a Professor in the Industrial Engineering & Management Sciences department of Northwestern University. This one is about as obscure as it gets. Obviously he is a mathematician. Here’s his page.