Goal:
  
  P : elt -> elt -> Prop
  s : t
  H : forall v1 v2 : elt, In v1 s -> In v2 s -> P v1 v2
  x : elt
  H0 : In x s
  ============================
   (forall x0 : elt, In x0 s -> P x x0)


DEBUG:Going to execute:
match reverse goal with
           | |- ?X1 => <Coq.Init.Tauto.is_unit_or_eq> flags X1; constructor 1
           | H:?X1 |- _ => <Coq.Init.Tauto.is_empty> flags X1; elim H
           | _ => assumption
           end