Set: pp::colors
  Set: pp::unicode
  Imported 'Int'
  Proved: T1
Theorem T1 (a b : ℤ) (f : ℤ → ℤ) (assumption : a = b) : f (f a) = f (f b) :=
    Congr (Refl f) (Congr (Refl f) assumption)