Goal:
  
  P : E.t -> Prop
  P_Proper : Proper (E.eq ==> impl) P
  s : t
  x : elt
  xs : list elt
  H2 : P x
  H3 : forall x : elt, InA E.eq x xs -> P x
  H1 : Forall P xs
  H0 : forall x : elt, InA E.eq x xs -> P x
  x0 : elt
  H4 : E.eq x0 x
  ============================
   (P x0)


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 0: Backtrace:

P is used in conclusion.
Level 0: Backtrace:

P is used in conclusion.
Level 0: Backtrace:

P is used in conclusion.
Level 0: Backtrace:

P is used in conclusion.
Level 0: Backtrace:

P is used in conclusion.
Level 1: Backtrace:

P is used in conclusion.
Level 0: Backtrace:

P is used in conclusion.
Level 3: Backtrace:

Not convertible.
Level 3: Backtrace:

Not convertible.
Level 3: Backtrace:

Not convertible.
Level 2: Backtrace:

Not convertible.