congr! 1
σ : Instantiation
τ τ' : MetaInstantiation
x : VarName
phi : Formula
phi_ih : phi.metaVarSet = ∅ → sub σ τ phi = sub σ τ' phi
h1 : phi.metaVarSet = ∅
⊢ forall_ (↑σ x) (sub σ τ phi) = forall_ (↑σ x) (sub σ τ' phi)
case h.e'_2
σ : Instantiation
τ τ' : MetaInstantiation
x : VarName
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