So this is basically the summary of these four steps. So once again, in the final step, in step four, the abstraction of two more hydrogen ions to a protons from the matrix helps oxidize the heme A three and the copper B group back to their original oxidized states. In the case of copper B, we basically oxidize it back into the copper two plus form. In the process, we also use those two protons to actually generate two water molecules. And this is basically the summary of these four steps that take place on complex four. So let's take a look at this summary.