And this is a diagram that describes the concerted model. Now, the big point about the concerted model is hemoglobin can only exist in two states. It can either exist in the t state, the ten state, or it can exist in the r state, the relaxed state. And by binding oxygen onto that hemoglobin molecule, all we're doing according to this model is shifting the equilibrium between the two states. And to see what we mean, let's take a look at the left side of this diagram. So on the left side, right here, none of the heme groups on the hemoglobin actually contain oxygen.