In a world of four people or a pool of four people, how many ways can you choose two? How many ways to choose two? Because that's what we're doing. Each handshake is just really a selection of two of these people. And so we want to say how many ways can we select two people so that we have a different, each combination, each of these ways to select two people should have a different combination of people in it. If two of them had the same, if A, B, and B, A, these are the same combination. And so this is really a combinations problem.