cases h1
P : PredName
zs : List VarName
H phi psi : Formula
phi_ih : phi.predVarSet = ∅ → replace P zs H phi = phi
psi_ih : psi.predVarSet = ∅ → replace P zs H psi = psi
h1 : phi.predVarSet = ∅ ∧ psi.predVarSet = ∅
⊢ replace P zs H (phi.iff_ psi) = phi.iff_ psi
case intro
P : PredName
zs : List VarName
H phi psi : Formula
phi_ih : phi.predVarSet = ∅ → replace P zs H phi = phi
psi_ih : psi.predVarSet = ∅ → replace P zs H psi = psi
left✝ : phi.predVarSet = ∅
right✝ : psi.predVarSet = ∅
⊢ replace P zs H (phi.iff_ psi) = phi.iff_ psi