Set: pp::colors
  Set: pp::unicode
  Imported 'macros'
  Proved: T
theorem T (A : Type)
    (p : A → Bool)
    (f : A → A → A)
    (x y z : A)
    (H1 : p (f x x))
    (H2 : x = y)
    (H3 : x = z) : p (f y z) :=
    subst (subst H1 H2) H3