Inductive stepN x y y': nat -> Prop :=
    | trivial_step: y = y' -> stepN x y y' 0
    | _stepN n _y: int_step x y _y -> stepN x _y y' n -> stepN x y y' (S n).Inductive stepN x y y': nat -> Prop :=
    | trivial_step: y = y' -> stepN x y y' 0
    | _stepN n _y: int_step x y _y -> stepN x _y y' n -> stepN x y y' (S n).Inductive stepN x y y': nat -> Prop :=
    | trivial_step: y = y' -> stepN x y y' 0
    | _stepN n _y: int_step x y _y -> stepN x _y y' n -> stepN x y y' (S n).(** *Safety with stepN *)
    Inductive exp_safetyN_gen {_exp_safety} (x:X) (y:Y): Prop:=
    | paco_halted_safetyN : halted x y -> exp_safetyN_gen x y
    | paco_internal_safetyN y' n: stepN x y y' (S n)  ->
                                  (forall x',  valid x' y' -> _exp_safety x' y') ->
                                  exp_safetyN_gen x y
    | paco_external_safetyN x' y': ext_step x y x' y' ->
                                   (forall x',  valid x' y' -> _exp_safety x' y') ->
                                   exp_safetyN_gen x y.(** *Safety with stepN *)
    Inductive exp_safetyN_gen {_exp_safety} (x:X) (y:Y): Prop:=
    | paco_halted_safetyN : halted x y -> exp_safetyN_gen x y
    | paco_internal_safetyN y' n: stepN x y y' (S n)  ->
                                  (forall x',  valid x' y' -> _exp_safety x' y') ->
                                  exp_safetyN_gen x y
    | paco_external_safetyN x' y': ext_step x y x' y' ->
                                   (forall x',  valid x' y' -> _exp_safety x' y') ->
                                   exp_safetyN_gen x y.(** *Safety with stepN *)
    Inductive exp_safetyN_gen {_exp_safety} (x:X) (y:Y): Prop:=
    | paco_halted_safetyN : halted x y -> exp_safetyN_gen x y
    | paco_internal_safetyN y' n: stepN x y y' (S n)  ->
                                  (forall x',  valid x' y' -> _exp_safety x' y') ->
                                  exp_safetyN_gen x y
    | paco_external_safetyN x' y': ext_step x y x' y' ->
                                   (forall x',  valid x' y' -> _exp_safety x' y') ->
                                   exp_safetyN_gen x y.(** *Safety with stepN *)
    Inductive exp_safetyN_gen {_exp_safety} (x:X) (y:Y): Prop:=
    | paco_halted_safetyN : halted x y -> exp_safetyN_gen x y
    | paco_internal_safetyN y' n: stepN x y y' (S n)  ->
                                  (forall x',  valid x' y' -> _exp_safety x' y') ->
                                  exp_safetyN_gen x y
    | paco_external_safetyN x' y': ext_step x y x' y' ->
                                   (forall x',  valid x' y' -> _exp_safety x' y') ->
                                   exp_safetyN_gen x y.Definition paco_exp_safetyN := paco2 (@exp_safetyN_gen).

Lemma valid_stepN: forall n, forall x y y', valid x y -> stepN x y y' n -> valid x y'.