Hint Resolve lexfg_lambda.

(* Specifications: *)
Theorem lexfg_env_t :
forall (a a' : terms) (s : sub_explicits),
e_lexfg _ (e_P1 wt) (e_P2 wt) a a' ->
e_lexfg _ (e_P1 wt) (e_P2 wt) (env a s) (env a' s).