intros a p H'; red in |- *; intros H'0; inversion H'.
generalize H0; simpl in |- *; intuition; auto.
Qed.

Theorem canonical_cons :
forall l a b,
ltT b a ->
~ zeroP (A:=A) A0 eqA (n:=n) a ->
canonical (pX b l) -> canonical (pX a (pX b l)).