Definition of a Generator

First, we consider one functional group. The distribution of reactants is very simple in this case because there is only one probability a (the functional group has bound another monomer unit) and a probability 1 - a (no unit is bound). The definition of a generating function requires that the probability for no event has to be multiplied by s° = 1, and the probability for one event by s1 = s hence, the p.g.f for one functional group A... 

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