fact: Fixpoint filter_option {A} (l: list (option A)) : list A := match l with | nil => nil | Some x :: l' => x :: filter_option l' | None :: l' => filter_option l' end.
imports: Coq.Lists.List Coq.micromega.Lia Coq.Sorting.Permutation Coq.ZArith.ZArith_base Coq.ZArith.Zcomplements Coq.Logic.FunctionalExtensionality CertiGraph.lib.Coqlib CertiGraph.lib.EquivDec_ext VST.zlist.sublist VST.zlist.list_solver