Inductive Psatz : Type :=
| PsatzLet: Psatz -> Psatz -> Psatz
| PsatzIn : nat -> Psatz
| PsatzSquare : PolC -> Psatz
| PsatzMulC : PolC -> Psatz -> Psatz
| PsatzMulE : Psatz -> Psatz -> Psatz
| PsatzAdd  : Psatz -> Psatz -> Psatz
| PsatzC    : C -> Psatz
| PsatzZ    : Psatz.
Register PsatzLet    as micromega.Psatz.PsatzLet.
Register PsatzIn     as micromega.Psatz.PsatzIn.
Register PsatzSquare as micromega.Psatz.PsatzSquare.
Register PsatzMulC   as micromega.Psatz.PsatzMulC.
Register PsatzMulE   as micromega.Psatz.PsatzMulE.
Register PsatzAdd    as micromega.Psatz.PsatzAdd.
Register PsatzC      as micromega.Psatz.PsatzC.
Register PsatzZ      as micromega.Psatz.PsatzZ.
(** Given a list [l] of NFormula and an extended polynomial expression [e], if [eval_Psatz l e] succeeds (= Some f) then [f] is a logic consequence of the conjunction of the formulae in l. Moreover, the polynomial expression is obtained by replacing the (PsatzIn n) by the nth polynomial expression in [l] and the sign is computed by the "rule of sign" *)
(* Might be defined elsewhere *)
Definition map_option (A B:Type) (f : A -> option B) (o : option A) : option B :=
match o with
| None => None
| Some x => f x
end.
Arguments map_option [A B] f o.
Definition map_option2 (A B C : Type) (f : A -> B -> option C)
(o: option A) (o': option B) : option C :=
match o , o' with
| None , _ => None
| _ , None => None
| Some x , Some x' => f x x'
end.
Arguments map_option2 [A B C] f o o'.
Definition Rops_wd := mk_reqe (*rplus rtimes ropp req*)
(SORplus_wd sor)
(SORtimes_wd sor)
(SORopp_wd sor).
Definition pexpr_times_nformula (e: PolC) (f : NFormula) : option NFormula :=
let (ef,o) := f in
match o with
| Equal => Some (Pmul cO cI cplus ctimes ceqb e ef , Equal)
|   _   => None
end.
Definition nformula_times_nformula (f1 f2 : NFormula) : option NFormula :=
let (e1,o1) := f1 in
let (e2,o2) := f2 in
map_option  (fun x => (Some (Pmul cO cI cplus ctimes ceqb e1 e2,x)))    (OpMult o1 o2).
Definition nformula_plus_nformula (f1 f2 : NFormula) : option NFormula :=
let (e1,o1) := f1 in
let (e2,o2) := f2 in
map_option  (fun x => (Some (Padd cO cplus ceqb e1 e2,x)))    (OpAdd o1 o2).
Fixpoint eval_Psatz (l : list NFormula) (e : Psatz) {struct e} : option NFormula :=
match e with
| PsatzLet p1 p2 => match eval_Psatz l p1 with
| None => None
| Some f => eval_Psatz (f::l) p2
end
| PsatzIn n => Some (nth n l (Pc cO, Equal))
| PsatzSquare e => Some (Psquare cO cI cplus ctimes ceqb e  , NonStrict)
| PsatzMulC re e => map_option (pexpr_times_nformula re) (eval_Psatz l e)
| PsatzMulE f1 f2 => map_option2 nformula_times_nformula  (eval_Psatz l f1) (eval_Psatz l f2)
| PsatzAdd f1 f2  => map_option2 nformula_plus_nformula  (eval_Psatz l f1) (eval_Psatz l f2)
| PsatzC  c  => if cltb cO c then Some (Pc c, Strict) else None
(* This could be 0, or <> 0 -- but these cases are useless *)
| PsatzZ     => Some (Pc cO, Equal) (* Just to make life easier *)
end.

Lemma nformula_plus_nformula_correct : forall (env:PolEnv)
(f1 f2 f : NFormula),
eval_nformula env f1 -> eval_nformula env f2 ->
nformula_plus_nformula f1 f2 = Some f  ->
eval_nformula env f.