Set: pp::colors
  Set: pp::unicode
  Assumed: a
  Assumed: b
  Assumed: f
λ x : ℕ, x = 1 ∧ f (λ y z : ℕ, y + z > 1)
funext (λ x : ℕ,
          and_congrr
              (λ C::2 : f (λ y z : ℕ, y + z > x), refl (x = 1))
              (λ C::9 : x = 1, congr2 f (funext (λ y : ℕ, funext (λ z : ℕ, congr2 (Nat::gt (y + z)) C::9)))))