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


DEBUG:Going to execute:
inversion 1
Level 0: Backtrace:

Unable to find an instance for the variable x.
Level 0: Backtrace:

Unable to find an instance for the variable x.