Goal:
  
  A : Type
  P : A → A → Prop
  r : A
  r' : A
  H : Forall2 P [r] [r']
  H3 : P r r'
  H5 : Forall2 P [] []
  ============================
   (P r r')


DEBUG:Going to execute:
F x2 x1 x0
Level 2: evaluation returns
<coq-core.plugins.tauto::find_cut@0>
where
k := fun id0 id1 X2 => assert X2; [ exact (id0 id1) | clear id0 ]
     where
     flags := 
     of type
     tauto_flags
of type
tacvalue of type tacvalue