B, whether A's and B's are functions of the canonical variables, the q's and p's which we take over from classical mechanics, then, quantum mechanics will tell you that this is greater than or equal to on the right hand side, a certain quantity which is associated with A and B. It will turn out to be this is greater than equal to one half the modulus of the expectation value of the Poisson bracket of quantum bracket, that is, Poisson bracket of A with B, which turns out to be the commutator and I am going to define what it means. 