∀ {α : Type u} {β : α → Type v} [inst : BEq α] [inst_1 : Hashable α] [EquivBEq α] [LawfulHashable α]
  {l : List ((a : α) × β a)},
  List.Pairwise (fun a b => (a.fst == b.fst) = false) l →
    (↑↑(Std.DHashMap.Internal.Raw₀.emptyWithCapacity.insertMany l)).size = l.length