simp
z X : String
vs : List Var
j : ℕ
⊢ (List.map (Var.close j (free_ z)) vs).toFinset.biUnion Var.freeVarSet ⊆ vs.toFinset.biUnion Var.freeVarSet \ {free_ z}
z X : String
vs : List Var
j : ℕ
⊢ ∀ a ∈ vs, (Var.close j (free_ z) a).freeVarSet ⊆ vs.toFinset.biUnion Var.freeVarSet \ {free_ z}