simp
X : String
vs : List Var
x : String
a2_left : free_ x ∈ vs
a1 : ∃ a ∈ vs, free_ x ∈ a.freeVarSet
⊢ free_ x ∈ vs ∧ True
X : String
vs : List Var
x : String
a2_left : free_ x ∈ vs
a1 : ∃ a ∈ vs, free_ x ∈ a.freeVarSet
⊢ free_ x ∈ vs