∀ {α : Type u} {x : BEq α} {x_1 : Hashable α} {m : Std.ExtDHashMap α fun x => Unit} [inst : EquivBEq α]
  [inst_1 : LawfulHashable α] {l : List α} {k k' : α},
  (k == k') = true →
    k ∉ m →
      List.Pairwise (fun a b => (a == b) = false) l →
        k ∈ l → (Std.ExtDHashMap.Const.insertManyIfNewUnit m l).getKey? k' = some k