intros p q; case p; case q; unfold lex_exp in |- *; simpl in |- *; auto.
Qed.
Hint Resolve fsltP.

Theorem sltp_wf : well_founded sltP.
lapply (wf_inverse_image poly (Pow _ ltM) (lex_exp _ ltM) fspoly);
[ intros H'3 | idtac ].