∀ {p : Prop} {α : Sort u_1} [inst : Countable α] {a b : α} {m n : ℕ},
  (a = b → m = n → p) →
    Nat.pair (Mathlib.Deriving.Countable.encode✝ a) m = Nat.pair (Mathlib.Deriving.Countable.encode✝¹ b) n → p