(2) P ±,P ± . The relevant N * P + = N P -1 is decremented for this cluster, because this doubly-paired cluster takes up two monomer sites. However, in a transfer matrix formalism we would obtain this cluster integral in two steps (B 0± φ P ± × F ± ), automatically accounting for this additional 'space' along the chain. If the subsequent monomer along the chain is also paired, then we can obtain the cluster integral in three steps (B 0± φ P ± ×F ± ×E ± ), and so on. The two-particle connected diagrams can thus be written using the transfer matrix formalism described in Equations 45 and 46. We merely use the definitions already given and A = A 0,± φ ± , B = B 0,± φ P ± , and D = 1.