Before revision:  The first is based on different kinetic barriers , and is characterized by a high speed and high dissipation close to the lowest possible error. The second is based on energy differences between right and wrong copies, and is characterized by the fact that minimum copying error can be achieved at low speed and low dissipation. In models characterized by a single copying step, we demonstrate thatthese modes are alternative, i.e. they cannot be mixed to further reduce the minimum error .
After revision:  The first is based on different kinetic barriers or different binding energy of the two matches. We demonstrate that, in single-step reactions, the two discrimination mechanisms are strictly alternative and can not be mixed to further reduce the minimum error .