congr! 1
σ : Instantiation
τ τ' : MetaInstantiation
phi : Formula
phi_ih : phi.metaVarSet = ∅ → sub σ τ phi = sub σ τ' phi
h1 : phi.metaVarSet = ∅
⊢ (sub σ τ phi).not_ = (sub σ τ' phi).not_
case h.e'_1
σ : Instantiation
τ τ' : MetaInstantiation
phi : Formula
phi_ih : phi.metaVarSet = ∅ → sub σ τ phi = sub σ τ' phi
h1 : phi.metaVarSet = ∅
⊢ sub σ τ phi = sub σ τ' phi