Set: pp::colors
  Set: pp::unicode
  Assumed: f
  Assumed: P
  Assumed: Ax1
  Proved: T1
  Assumed: b
  Assumed: Ax2
  Proved: T2
Theorem T2 (a : ℤ) : (P a a) ⇒ (f a a) := Discharge (λ H : P a a, Ax1 a a H)