(***************************************************************************  Main theorem  ***************************************************************************)
Ltac uneval :=
repeat match goal with
| |- context [ ?x @ ?l * ?y @ ?l ] => change (x@l * y@l) with ((x*y)@l)
| |- context [ ?x @ ?l + ?y @ ?l ] => change (x@l + y@l) with ((x+y)@l)
end.

Theorem Fnorm_crossproduct l fe1 fe2 :
let nfe1 := Fnorm fe1 in
let nfe2 := Fnorm fe2 in
(num nfe1 * denum nfe2) @ l == (num nfe2 * denum nfe1) @ l ->
PCond l (condition nfe1 ++ condition nfe2) ->
FEeval l fe1 == FEeval l fe2.