But I didn't.

Today in one of my math classes, the professor was defining the division algorithm for polynomials: if f and g are polynomials, then there exist polynomials p and r, with either r = 0 or deg(r) < deg(g), such that f = p*g + r.

He wanted to use the letter q for "quotient" instead of p, but thought that it would get confusing because it would look too similar to g on the chalkboard. But during part of his proof, he started writing down q anyways--he did this several times until he realized his mistake.

I so very much wanted to advise him to "mind his p's and q's."