(* Advanced inversion lemmas ************************************************)
lemma lfxs_inv_frees: ∀R,L1,L2,T. L1 ⪤*[R, T] L2 →
(* Advanced inversion lemmas ************************************************)
lemma lfxs_inv_frees: ∀R,L1,L2,T. L1 ⪤*[R, T] L2 →