Since equations (13a) and (13b) are only valid after the initial fast transient, t c1 , it is necessary to define a boundary condition for s 1 at t = t c1 . We will assume that there is a negligible decrease in s 1 during the initial buildup of c 1 . This is equivalent to the initial experimental condition for the initial rate or time course experiments. The assumption that the depletion of s 1 is negligible over the fast transient is known as the RSA. Formally, the RSA is