Goal:
  
  P : E.t -> Prop
  P_Proper : Proper (E.eq ==> impl) P
  s : t
  x : elt
  xs : list elt
  IH : List.Exists P xs <-> (exists x : elt, InA E.eq x xs /\ P x)
  ============================
   (P x \/ (exists x : elt, InA E.eq x xs /\ P x) <->
    (exists x0 : elt, (E.eq x0 x \/ InA E.eq x0 xs) /\ P x0))


DEBUG:Going to execute:
<coq-core.plugins.firstorder::firstorder@0> $1 $2
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH
DEBUG LTAC Evaluated term: IH

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