Fixpoint Fnorm (e : FExpr) : linear :=
match e with
| FEO => mk_linear 0 1 nil
| FEI => mk_linear 1 1 nil
| FEc c => mk_linear (PEc c) 1 nil
| FEX x => mk_linear (PEX C x) 1 nil
| FEadd e1 e2 =>
let x := Fnorm e1 in
let y := Fnorm e2 in
let s := split (denum x) (denum y) in
mk_linear
((num x ** right s) ++ (num y ** left s))
(left s ** (right s ** common s))
(condition x ++ condition y)%list
| FEsub e1 e2 =>
let x := Fnorm e1 in
let y := Fnorm e2 in
let s := split (denum x) (denum y) in
mk_linear
((num x ** right s) -- (num y ** left s))
(left s ** (right s ** common s))
(condition x ++ condition y)%list
| FEmul e1 e2 =>
let x := Fnorm e1 in
let y := Fnorm e2 in
let s1 := split (num x) (denum y) in
let s2 := split (num y) (denum x) in
mk_linear (left s1 ** left s2)
(right s2 ** right s1)
(condition x ++ condition y)%list
| FEopp e1 =>
let x := Fnorm e1 in
mk_linear (NPEopp (num x)) (denum x) (condition x)
| FEinv e1 =>
let x := Fnorm e1 in
mk_linear (denum x) (num x) (num x :: condition x)
| FEdiv e1 e2 =>
let x := Fnorm e1 in
let y := Fnorm e2 in
let s1 := split (num x) (num y) in
let s2 := split (denum x) (denum y) in
mk_linear (left s1 ** right s2)
(left s2 ** right s1)
(num y :: condition x ++ condition y)%list
| FEpow e1 n =>
let x := Fnorm e1 in
mk_linear ((num x)^^n) ((denum x)^^n) (condition x)
end.
(* Example *)
(* Eval compute in (Fnorm (FEdiv (FEc cI) (FEadd (FEinv (FEX xH%positive)) (FEinv (FEX (xO xH)%positive))))). *)

Theorem Pcond_Fnorm l e :
PCond l (condition (Fnorm e)) ->  ~ (denum (Fnorm e))@l == 0.