So we have one H plus ion coming in. We take off one H atom from this nitrogen and we use this oxygen to basically form this water molecule. In the process, we form a sigma bond between this nitrogen and this carbon. So we close this structure to form this ring. Now, in the next step, we have a reduction step, we have an oxidation reduction reaction in which we have this NAD plus that we use to take electrons from these atoms here, from these carbon atoms here. And we essentially form a pi bond between this carbon here and this carbon here.