simp [fvUnivClosure, ←Rew.hom_comp_app, Rew.eq_empty]
ξ : Type u_1
L : Language
h : IsEmpty ξ
inst✝ : DecidableEq ξ
σ : Formula L ξ
⊢ ∀ᶠ* σ = ∀' Rew.empty.hom σ
ξ : Type u_1
L : Language
h : IsEmpty ξ
inst✝ : DecidableEq ξ
σ : Formula L ξ
⊢ ∀* Rew.empty.hom σ = ∀' Rew.empty.hom σ