It initially is a square, and it still is a square. Now, we know experimentally in nature, as soon as that oxygen binds onto that hemegroom of that polypeptide, that changes the confirmation of that polypeptide. And this simply is not what we see according to this diagram. In fact, what we also see in nature is when one of the heme groups binds that oxygen, the adjacent heme groups are also affected. They increase their affinity for oxygen because they change their shape as well. And this is something that we don't see according to this model.