fact: Definition boxed_option {A} (P: A -> Prop) (x: @IndexedElement A) := Pick (fun l : list A => (P (indexedElement x) -> ret [indexedElement x] ↝ l) /\ (~ P (indexedElement x) -> l = [])).
imports: Coq.Lists.List Coq.Program.Program Coq.Sets.Ensembles Fiat.Common Fiat.Common.List.ListFacts Fiat.Common.List.ListMorphisms Fiat.Common.Ensembles.IndexedEnsembles Fiat.Common.DecideableEnsembles Fiat.Computation