11. These axiom schemas are chosen to enable one to derive the deduction theorem from them easily. 12. In the metavariable sense, a predicate variable can be used to define an axiom schema . 13. Proof rules with zero antecedents are also called " axioms " or " axiom schemas ". 14. Burgess's theory ST is GST with Null Set replacing the axiom schema of specification. 15. The axiom schema of replacement is not necessary for the proofs of most theorems of ordinary mathematics. 16. For existence, we will use the Axiom of Infinity combined with the Axiom schema of specification. 17. The axioms of this section may replace the Axiom Schema of Class Comprehension in the preceding section. 18. The only entity specific to Boolean algebras is axiom schema "'A1 " '. 19. The resulting axiom schema is also called the "'axiom schema of boundedness " '. 20. The resulting axiom schema is also called the "'axiom schema of boundedness " '.
