intros Q a b H' q H'0.
apply pick_inv_eqT_lem with (Q := Q) (p := pX b q) (q := q); auto.
Qed.

(* Specifications: *)
Theorem reducehead_imp_reduce :
forall (Q : list (poly A0 eqA ltM)) (p q : list (Term A n)),
reducehead Q p q -> reduce Q p q.