Set: pp::colors
  Set: pp::unicode
  Set: pp::colors
  Assumed: N
  Assumed: a
  Assumed: b
  Assumed: c
  Assumed: P
  Proved: T1
Theorem T1 (f : N → N) (H : P (f a) b (f (f c))) : ∃ x y z : N, P x y z :=
    ExistsIntro (f a) (ExistsIntro b (ExistsIntro (f (f c)) H))