When monomers with two types of functional groups A and B undergo step growth polymerisation by virtue of a reaction between A and B groups, a similar analytical results are known. See the table on the right for several examples. In this case,  is the fraction of initial monomers with  groups A and  groups B. Suppose that A is the group that is depleted first. Random graph theory states that gelation takes place when , where the gelation conversion is  and . Molecular size distribution, the molecular weight averages, and the distribution of gyration radii have known formal analytical expressions. When degree distribution , giving the fraction of monomers in the network with  neighbours connected via A group and  connected via B group at time  is solved numerically, the gel state is detected when , where  and .