Quotation about usefulness of good definitions in maths?

Question

I feel like I have heard this quote somewhere, but can't remember where or by whom. I saw somewhere on this site something along the lines of "a good definition is worth a thousand proofs", but that doesn't sound quite right and was unattributed. Anyone know what I'm talking about?

Answer 1

You know what, it was probably this:

A good lemma is worth a thousand theorems.