Goal:
  
  P : E.t -> Prop
  P_Proper : Proper (E.eq ==> impl) P
  s : t
  x : elt
  xs : list elt
  H0 : forall x : elt,
       (fun x0 : elt => InA E.eq x0 xs /\ P x0) x -> List.Exists P xs
  x0 : elt
  H1 : InA E.eq x0 xs
  H2 : P x0
  H3 : forall y : E.t, E.eq x0 y -> impl (P x0) (P y)
  H4 : List.Exists P xs
  x1 : elt
  H : InA E.eq x1 xs
  H5 : P x1
  ============================
   (E.eq x0 x)


DEBUG:Going to execute:
<Coq.Init.Tauto.simplif> flags;
            <Coq.Init.Tauto.axioms> flags ||
              match reverse goal with
              | id:(?X1 -> ?X2) -> ?X3
                |- _ =>
                    cut X3;
                     [ intro; clear id; t_tauto_intuit
                     | cut (X1 -> X2);
                        [ exact
                        id
                        | generalize (fun y : X2 => id (fun x : X1 => y));
                           intro; clear id; (solve 
                           [ t_tauto_intuit ]) ] ]
              | id:~ ?X1 -> ?X3
                |- _ =>
                    cut X3;
                     [ intro; clear id; t_tauto_intuit
                     | cut (~ X1);
                        [ exact
                        id
                        | clear id; intro; (solve [ t_tauto_intuit ]) ] ]
              | |- ?X1 =>
                    <Coq.Init.Tauto.is_disj> flags X1; (solve
                     [ left; t_tauto_intuit | right; t_tauto_intuit ])
              end ||
                match goal with
                | |- _ -> _ => intro; t_tauto_intuit
                | |- _ => t_reduce; t_solver
                end || t_solver