 Among the points in favour of weaker systems is that, unlike \(\mathbf{R}\) or \(\mathbf{E}\), many of them are decidable. Another feature of some of these weaker logics that makes them attractive is that they can be used to construct a naïve set theory. A naïve set theory is a theory of sets that includes as a theorem the naïve comprehension axiom, viz., for all formulae \(A(y)\),