fact: Definition union_map (A:Set) (f:A -> vars) (l:list A) := (List.fold_right (fun t acc => f t \u acc) {}) l.
imports: Coq.Arith.Arith Coq.FSets.FSets Coq.Lists.List Metalib.AssocList Metalib.CoqListFacts Metalib.LibTactics Metalib.MetatheoryAtom Metalib.CoqEqDec