The solid black curve is the numerically-computed solution to (49a)–(49d). The initial concentrations and rate constants used in the numerical simulation are: k1 = 1, k2 = 1, k−1 = 1, , , k−3 = 1, k3 = 1, k4 = 2 and (units have been omitted). s2 and c2 have been scaled by their numerically–obtained maximum values.