fact: Definition hd_rules_graph a1 a2 := In a1 D /\ In a2 D /\ exists p, exists s, S (sub s (rhs a1)) (sub s (shift p (lhs a2))).
imports: CoLoR(LogicUtil ATrs RelUtil RelSub SN AShift ADPGraph VecUtil ASubstitution) Coq(List Lia)