(* An unsatisfiable condition: issued when a division by zero is detected *)
Definition absurd_PCond := cons 0%poly nil.

Lemma absurd_PCond_bottom : forall l, ~ PCond l absurd_PCond.
Definition default_isIn e1 p1 e2 p2 :=
if PExpr_eq e1 e2 then
match Z.pos_sub p1 p2 with
| Zpos p => Some (Npos p, 1%poly)
| Z0 => Some (N0, 1%poly)
| Zneg p => Some (N0, e2 ^^ Npos p)
end
else None.