And this R state is described by this steep curve right over here. And to actually obtain that Sigmoidal curve that we actually see for the hemoglobin oxygen binding, we have to combine these two curves to basically get this Sigmoidal curve. So the Sigmoidal curve for hemoglobin is formed from the combination of the T state curve, this curve here, the shallow one, and the steep one, the R state curve. Now, the final thing I'd like to discuss about the Concerted model is what's the limitation of the Concerted model? What is the problem? Well, the problem is the following.