fact: Axiom disjoint_sym : forall A B (E : list (atom*A)) (F : list (atom*B)), disjoint E F <-> disjoint F E.
imports: Coq.FSets.FSets Coq.Lists.List Coq.Logic.Decidable Metalib.CoqFSetDecide Metalib.CoqListFacts Metalib.AssocList Metalib.MetatheoryAtom Metalib.LibTactics