∀ {α : Type u} {β : Type v} {m : Std.HashMap.Raw α β} [inst : BEq α] [inst_1 : Hashable α] [EquivBEq α]
  [LawfulHashable α],
  m.WF →
    ∀ {l : List (α × β)},
      List.Pairwise (fun a b => (a.1 == b.1) = false) l →
        (∀ a ∈ m, (List.map Prod.fst l).contains a = false) → (m.insertMany l).size = m.size + l.length