1. The problem statement, all variables and given/known data For the example that two spin systems in thermal contact and attain equilibrium, the product of the original multiplicity function will be the new total multiplicity function, Now, we want to find the probability of the system to be slightly deviated from the equilibrium. 2. Relevant equations They are attached. 3. The attempt at a solution I acknowledge that the multiplicity function is closely related to the probability of the system is found in some state. If I sum over all states of interest, we should obtain the solution. However, no matter how I sum them or integrate them, there is no form of the error function given. I wonder what should I do.