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


DEBUG:Going to execute:
<Coq.Init.Tauto.is_unit_or_eq> flags X1; cut X2;
            [ intro; clear id | cut X1; [ exact id | constructor 1; fail ] ]
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

Level 2: Backtrace:

Not convertible.
Level 2: Backtrace:

Not convertible.
Level 2: Backtrace:

Not convertible.
Level 1: Backtrace:

Not convertible.