refine (bind ξvars = fresh_lemma' _ y _ _ _ t H; _). apply FreshMon.
destruct ξvars as [ varstypes [ pf1[ pf2 pfdist]]].
refine (X_ ((update_xi ξ t (leaves varstypes)))
refine (bind ξvars = fresh_lemma' _ y _ _ _ t H; _). apply FreshMon.
destruct ξvars as [ varstypes [ pf1[ pf2 pfdist]]].
refine (X_ ((update_xi ξ t (leaves varstypes)))