Since \(Z_2\) is a natural and sufficient environment for many mathematical theorems, it is an appropriate framework for answering questions raised by the reverse mathematics program. The main (but not the only) distinctions that are made in reverse mathematics concern the amount of the Comprehension Principle that is needed in proving this or that mathematical result. In particular, the role of Arithmetic and \(\Pi^1_1\)-Comprehension Principles is clarified. The basic theory of real numbers ca