"Surely You're Joking, Mr. Feynman!", p72:
That book [Woods`Advanced Calculus]
also showed how to
differentiate parameters under the integral sign
--it's a certain operation. It turns out
that's not taught very much in the universities;
they don't emphasize it.
But I caught on how to use that method,
and I used that one damn tool again and again.
So because I was self-taught using that book,
I had peculiar methods of doing integrals.