Let the WKG be an undirected graph G = (V, E) where V is a set of concept nodes and E is a set of predicate edges (see Materials and Methods). Two nodes v, w 2 V are said to be adjacent if there is an edge between them (v, w) 2 E. They are said to be connected if there a sequence of n _ 2 nodes v = v1, v2, . . . vn = w, such that, for i = 1, . . ., n−1 the nodes vi and vi+1 are adjacent. The transitive closure of G is G_ = (V, E_) where the set of edges is closed under adjacency, that is, two nodes are adjacent in G_ iff they are connected in G via at least one path. This standard notion of closure has been extended to weighted graphs, allowing adjacency to be generalized by measures of path length [27], such as the semantic proximity for the WKG we introduce next.