Goal:
  
  P : elt -> elt -> Prop
  s : t
  H : forall x : elt, In x s -> forall x0 : elt, In x0 s -> P x x0
  v1 : elt
  ============================
   (forall v2 : elt, In v1 s -> In v2 s -> P v1 v2)


DEBUG:Going to execute:
F x2 x1 x0
Level 3: 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