intros p q a b H' H'0.
elim (multpf_head p q a b); [ intros c E; rewrite E | idtac | idtac ];
simpl in |- *; auto.
Qed.

Theorem multpf_comp :
forall p r : list (Term A n),
eqP A eqA n p r ->
forall q s : list (Term A n),
canonical A0 eqA ltM p ->
canonical A0 eqA ltM q ->
canonical A0 eqA ltM r ->
canonical A0 eqA ltM s ->
eqP A eqA n q s -> eqP A eqA n (multpf p q) (multpf r s).