2 ms·∀ X [ ∅ ∉ X ⟹ ∃ f : X → ⋃ X ∀ A ∈ X ( f ( A ) ∈ A ) ]by jjgreen 6y ago∀ X [ ∅ ∉ X ⟹ ∃ f : X → ⋃ X ∀ A ∈ X ( f ( A ) ∈ A ) ]