Set: pp::colors
  Set: pp::unicode
  Set: lean::pp::implicit
  Set: pp::colors
  Assumed: N
λ (a : N) (f : N → N) (H : f a == a),
  let calc1 : f a == a := @SubstP N (f a) a (λ x : N, f a == x) (@Refl N (f a)) H in calc1 :
    Π (a : N) (f : N → N), f a == a → f a == a