unfold qs.
fold raw_body.
rewrite fix_measure_utils.unfold.
rewrite <- bodies.
unfold qs. fold raw_body...
intros.
apply raw_body_ext.
intros.
destruct x. destruct y.
simpl in H0.
subst...
Qed.

Lemma toBody_cons (n: nat) (v: Vector.t X (S n)): body v = selectPivotPart v.
intros.