left
case h1
v t x : VarName
phi : Formula
phi_ih : ∀ (binders : Finset VarName), v ∈ binders → replaceFreeAux v t binders phi = phi
binders : Finset VarName
h1 : v ∈ binders
⊢ v ∈ binders ∨ v = x
case h1.h
v t x : VarName
phi : Formula
phi_ih : ∀ (binders : Finset VarName), v ∈ binders → replaceFreeAux v t binders phi = phi
binders : Finset VarName
h1 : v ∈ binders
⊢ v ∈ binders