Set: pp::colors
  Set: pp::unicode
  Set: lean::pp::implicit
  Set: pp::colors
  Assumed: N
  Defined: T
definition T (a : N) (f : N → N) (H : @eq N (f a) a) : @eq N (f (f a)) (f (f a)) :=
    @substp N (f a) a (λ x : N, @eq N (f (f a)) (f (f a))) (@refl N (f (f a))) H