∀ {α : Type u} {β : α → Type v} [inst : BEq α] [inst_1 : Hashable α] [inst_2 : LawfulBEq α] {l : List ((a : α) × β a)}
  {k k' : α} (k_beq : (k == k') = true) {v : β k} [inst_3 : Inhabited (β k')],
  List.Pairwise (fun a b => (a.fst == b.fst) = false) l →
    ⟨k, v⟩ ∈ l → (↑(Std.DHashMap.Internal.Raw₀.emptyWithCapacity.insertMany l)).get! k' = cast ⋯ v