“…When solving the query q(X), the following PDG and strata are computed for the new context [1] due to the assumption in rule (1,[]), which can be displayed by enabling verbose output (with /verbose on). DES> q(X) ... Info: Building hypothetical computation context [1] for: p(Y) :-t(Y), not r(Y). Info: PDG: Nodes: [p/1,q/1,r/1,s/1,t/1] Arcs : [p/1-r/1,p/1+t/1,q/1+s/1] Info: Strata: [(q/1,1),(r/1,1),(s/1,1),(t/1,1),(p/1,2)] ...…”