where O represents empty sites within the network that are not currently occupied by individuals, and the parameter ε = 0.8093 accounts for the clustering within lattice-based networks. House and Keeling [133] considered a model of infection transmission and contact tracing on a network, where the closure scheme for [ABC] triples was asymmetric in A and C-this allowed the natural conservation of quantities in a highly clustered system. The work on dynamical PGF models [129] can be seen as an elegant simplification of this pairwise approach that is valid for SIR-type infection dynamics on configuration model networks. The equations can be reformulated as S = g(θ),