Goal:
    P : E.t -> Prop  P_Proper : Proper (E.eq ==> impl) P  s : t
  ============================
   ((exists x : elt, InA E.eq x nil /\ P x) -> List.Exists P nil)


DEBUG:Going to execute:
solve
[ constructor | inversion 1 | intros [x [H H']]; inversion H ]