End Fcons_impl.
Section Fcons_simpl.
(* Some general simpifications of the condition: eliminate duplicates, split multiplications *)
Fixpoint Fcons (e:PExpr C) (l:list (PExpr C)) {struct l} : list (PExpr C) :=
match l with
nil       => cons e nil
| cons a l1 => if PExpr_eq e a then l else cons a (Fcons e l1)
end.

(* Specifications: *)
Theorem PFcons_fcons_inv:
forall l a l1, PCond l (Fcons a l1) ->  ~ a @ l == 0 /\ PCond l l1.