trans Var.freeVarSet v \ {free_ z}
z X : String
vs : List Var
j : ℕ
v : Var
a1 : v ∈ vs
⊢ (Var.close j (free_ z) v).freeVarSet ⊆ vs.toFinset.biUnion Var.freeVarSet \ {free_ z}
z X : String
vs : List Var
j : ℕ
v : Var
a1 : v ∈ vs
⊢ (Var.close j (free_ z) v).freeVarSet ⊆ v.freeVarSet \ {free_ z}

z X : String
vs : List Var
j : ℕ
v : Var
a1 : v ∈ vs
⊢ v.freeVarSet \ {free_ z} ⊆ vs.toFinset.biUnion Var.freeVarSet \ {free_ z}