tauto
v : Var
phi psi : Formula
phi_ih : occursIn v phi ∧ v.isFree ↔ v ∈ phi.freeVarSet
psi_ih : occursIn v psi ∧ v.isFree ↔ v ∈ psi.freeVarSet
⊢ (occursIn v phi ∨ occursIn v psi) ∧ v.isFree ↔ v ∈ phi.freeVarSet ∨ v ∈ psi.freeVarSet
no goals