 The earliest construction on Russell’s 1924 list is the famous “Frege/Russell definition” of numbers as classes of equinumerous classes from 1901 (Russell 1993, 320). The definition follows the example of the definitions of the notions of limit and continuity that were proposed for the calculus in the preceding century. Russell did not rest content with adopting the Peano axioms as the basis for the theory of the natural numbers and then showing how the properties of the numbers could be logically deduced from those axioms. Instead, he defined the basic notions of “number” , “successor” and “0” and proposed to show, with carefully chosen definitions of their basic notions in terms of logical notions, that those axioms could be derived from principles of logic alone. 