intro x _ a2 a3
v t : VarName
X : DefName
xs : List VarName
binders : Finset VarName
h1 : v ∈ binders
⊢ ∀ x ∈ xs, v = x → x ∉ binders → t = x
v t : VarName
X : DefName
xs : List VarName
binders : Finset VarName
h1 : v ∈ binders
x : VarName
a✝ : x ∈ xs
a2 : v = x
a3 : x ∉ binders
⊢ t = x