simp only [Var.lc_at] at a1
X : String
vs : List Var
j : ℕ
zs : List String
i i' : ℕ
a3_left : bound_ i' ∈ vs
a3_right : Var.openList j (List.map free_ zs) (bound_ i') = bound_ i
a1 : Var.lc_at (j + zs.length) (bound_ i')
⊢ i < j
X : String
vs : List Var
j : ℕ
zs : List String
i i' : ℕ
a3_left : bound_ i' ∈ vs
a3_right : Var.openList j (List.map free_ zs) (bound_ i') = bound_ i
a1 : i' < j + zs.length
⊢ i < j