Notation lexfg := (e_lexfg _) (only parsing).

Theorem lexfg_app_l : forall a a' b : terms, e_lexfg _ (e_P1 wt) (e_P2 wt) a a' -> e_lexfg _ (e_P1 wt) (e_P2 wt) (app a b) (app a' b).