∀ {α : Type u} {x : BEq α} {x_1 : Hashable α} {m : Std.ExtHashSet α} [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 → ∀ {h : k' ∈ m.insertMany l}, (m.insertMany l).get k' h = k