∀ {α : Type u} {x : BEq α} {x_1 : Hashable α} {β : Type v} [EquivBEq α] [LawfulHashable α] {l : List (α × β)} {k : α},
  (List.map Prod.fst l).contains k = false → (Std.DHashMap.Const.ofList l).getKey? k = none