simp only [Formula.freeVarSet]
z X : String
vs : List Var
j : ℕ
⊢ (pred_ X (List.map (Var.close j (free_ z)) vs)).freeVarSet ⊆ (pred_ X vs).freeVarSet \ {free_ z}
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}