simp
v t : VarName
phi psi : Formula
phi_ih : ¬isFreeIn v phi → fastReplaceFree v t phi = phi
psi_ih : ¬isFreeIn v psi → fastReplaceFree v t psi = psi
h1 : ¬(isFreeIn v phi ∨ isFreeIn v psi)
⊢ (fastReplaceFree v t phi).iff_ (fastReplaceFree v t psi) = phi.iff_ psi
v t : VarName
phi psi : Formula
phi_ih : ¬isFreeIn v phi → fastReplaceFree v t phi = phi
psi_ih : ¬isFreeIn v psi → fastReplaceFree v t psi = psi
h1 : ¬(isFreeIn v phi ∨ isFreeIn v psi)
⊢ fastReplaceFree v t phi = phi ∧ fastReplaceFree v t psi = psi