21. Virtually all mathematical theorems today can be formulated as theorems of set theory . 22. Other researchers have also modeled parametric polymorphism within constructive set theories . 23. This can be considered the central postulate of musical set theory . 24. In set theory , a singleton cannot be identified with its member. 25. The same is true of any consistent first order axiomatisation of set theory . 26. Peano arithmetic is equiconsistent with several weak systems of set theory . 27. Thus the axiom of choice is not generally available in constructive set theory . 28. Musical set theory provides concepts for categorizing musical objects and describing their relationships. 29. The first development of set theory was a naive set theory . 30. The first development of set theory was a naive set theory.
