Section Reduce.
Variable poly : Set.
Variable cb : list poly -> poly -> Prop.
Variable divp : poly -> poly -> Prop.
Variable reduce : list poly -> poly -> poly -> Prop.
Variable nf : list poly -> poly -> poly.
Variable stable : list poly -> list poly -> Prop.
Variable grobner : list poly -> Prop.
Variable zero : poly.
Variable zerop : poly -> Prop.
Variable zerop_dec : forall p : poly, {zerop p} + {~ zerop p}.
Hypothesis cb_id : forall (L : list poly) (p : poly), In p L -> cb L p.
Hypothesis cb_zerop : forall (L : list poly) (p : poly), zerop p -> cb L p.
Hypothesis
cb_incl :
forall (L1 L2 : list poly) (p : poly), incl L1 L2 -> cb L1 p -> cb L2 p.
Hypothesis nf_cb : forall (p : poly) (L : list poly), cb (p :: L) (nf L p).
Hypothesis
cb_trans :
forall (L : list poly) (p q : poly), cb (p :: L) q -> cb L p -> cb L q.
Hypothesis
cb_comp :
forall L1 L2 : list poly,
(forall p : poly, In p L1 -> cb L2 p) ->
forall q : poly, cb L1 q -> cb L2 q.
Hypothesis cb_nf : forall (p : poly) (L : list poly), cb (nf L p :: L) p.
Hypothesis
cb_compo :
forall (p : poly) (L1 : list poly),
cb L1 p ->
forall L2 : list poly, (forall q : poly, In q L1 -> cb L2 q) -> cb L2 p.
Hypothesis
zerop_elim_cb :
forall (L : list poly) (p q : poly), zerop p -> cb (p :: L) q -> cb L q.
Hypothesis
grobner_def :
forall L : list poly,
grobner L ->
forall p : poly, cb L p -> zerop p \/ (exists q : poly, reduce L p q).
Hypothesis
def_grobner :
forall L : list poly,
(forall p : poly, cb L p -> zerop p \/ (exists q : poly, reduce L p q)) ->
grobner L.
Hypothesis
nf_div :
forall (p : poly) (L : list poly),
~ zerop p ->
~ zerop (nf L p) ->
exists q : poly, In q (nf L p :: L) /\ divp p q /\ ~ zerop q.
Hypothesis
div_reduce :
forall (p : poly) (L1 L2 : list poly),
(forall r1 : poly,
In r1 L1 -> ~ zerop r1 -> exists r2 : poly, In r2 L2 /\ divp r1 r2) ->
forall q : poly, reduce L1 p q -> exists r : poly, reduce L2 p r.
Hypothesis divp_id : forall p : poly, divp p p.
Hypothesis divp_trans : transitive poly divp.
Hypothesis
nf_div_zero :
forall (p : poly) (L : list poly),
~ zerop p ->
zerop (nf L p) -> exists q : poly, In q L /\ divp p q /\ ~ zerop q.
intros L p H'.
apply zerop_elim_cb with (p := nf L p); auto.
Qed.
Hint Resolve zerop_nf_cb.
Definition redacc : list poly -> list poly -> list poly.
intros H'; elim H'.
intros L; exact (nil (A:=poly)).
intros a p Rec Acc.
apply LetP with (A := poly) (h := nf (p ++ Acc) a).
intros u H'0; case (zerop_dec u); intros Z.
exact (Rec Acc).
exact (u :: Rec (u :: Acc)).
Defined.
Definition red (L : list poly) : list poly := redacc L nil.
Hint Resolve incl_refl incl_tl incl_appr incl_appl incl_cons incl_app
in_or_app.
intros L1; elim L1; auto.
simpl in |- *; auto.
simpl in |- *; unfold LetP in |- *; intros a l H' L2 p.
case (zerop_dec (nf (l ++ L2) a)).
intros H'0 H'1.
apply cb_incl with (L1 := l ++ L2); auto.
simpl in |- *.
intros H'0 H'1; case H'1;
[ intros H'2; rewrite <- H'2; clear H'1 | intros H'2; clear H'1 ];
auto.
apply cb_trans with (p := nf (l ++ L2) a); auto.
apply cb_incl with (L1 := l ++ nf (l ++ L2) a :: L2); auto.
apply incl_app; auto with datatypes.
Qed.
unfold red in |- *.
intros L p H'.
generalize (redacc_cb L nil); simpl in |- *; auto.
rewrite <- app_nil_end; auto.
Qed.
intros L1; elim L1; simpl in |- *; auto.
intros L2 p H'; elim H'; auto.
unfold LetP in |- *.
intros a l H' L2 p H'0; case H'0;
[ intros H'1; rewrite H'1; clear H'0 | intros H'1; clear H'0 ];
auto.
case (zerop_dec (nf (l ++ L2) p)); auto.
intros H'0.
apply cb_comp with (L1 := l ++ L2); auto.
intros p0 H'2.
lapply (in_app_or l L2 p0); auto.
intros H'3; case H'3; auto.
intros H'0.
2: case (zerop_dec (nf (l ++ L2) a)); auto.
2: intros H'0.
2: apply
cb_incl
with (L1 := redacc l (nf (l ++ L2) a :: L2) ++ nf (l ++ L2) a :: L2);
auto with datatypes.
apply cb_compo with (L1 := nf (l ++ L2) p :: l ++ L2); simpl in |- *; auto.
intros q H'2; case H'2;
[ intros H'3; rewrite <- H'3; clear H'2 | intros H'3; clear H'2 ];
auto with datatypes.
case (in_app_or l L2 q H'3); auto with datatypes.
intros H'2.
apply
cb_incl with (L1 := redacc l (nf (l ++ L2) p :: L2) ++ nf (l ++ L2) p :: L2);
auto with datatypes.
Qed.
intros L p H'.
lapply (cb_redacc L nil p); [ intros H'3; generalize H'3 | idtac ];
simpl in |- *; auto.
rewrite <- app_nil_end; auto.
Qed.
intros p L H'.
apply cb_compo with (L1 := L); auto.
intros q H'0.
apply cb_red; auto.
Qed.
intros p L H'.
apply cb_compo with (L1 := red L); auto.
intros q H'0.
apply red_cb; auto.
Qed.
Hypothesis
nf_div_zero1 :
forall (p : poly) (L : list poly),
~ zerop p ->
zerop (nf L p) -> ex (fun q : poly => In q L /\ divp p q /\ ~ zerop q).

Theorem redacc_divp :
forall (L1 L2 : list poly) (p : poly),
~ zerop p ->
In p (L1 ++ L2) ->
exists q : poly, In q (redacc L1 L2 ++ L2) /\ divp p q /\ ~ zerop q.