The process of building the enumeration tree for the input graph in Figure1. The rhombus represents the root of the tree. The circles represent the genes inserted into the tree. The squares represent the leaves which store two sets of miRNAs – human and viral (H(T) and V(T)). These miRNAs target at least |T|−ϵ
genes in T respectively, where T is the set of genes in the path from the leaf to the root. Viral miRNAs are labeled with uppercase letters and the human miRNAs are labeled with numbers. The rectangles (see legend) indicate paths that are pruned from the tree for one of two reasons: (1) paths where the miRNAs in the leaf break the quorum are in solid rectangles (in this example the required quorum is 3 for viral miRNAs and 4 for human miRNAs); (2) paths where at least one gene or a pair of genes do not satisfy the error constraint with respect to the miRNAs in the leaf are in dotted rectangles. Paths which reach the minimal number of genes, (in this example the number is 3), are forwarded to the next step of generating modules. The three sub-figures (a), (b) and (c) show the insertion of genes a, e, b, d and c, into the tree, in this order.