Partial recursive functions and ω-functions
Charles H. Applebaum, J. C. E. Dekker · Journal of Symbolic Logic · 1970
Let ε stand for the set of all numbers (i.e., nonnegative integers), V for the class of all sets (i.e., subcollections of ε) and for the family of all functions (i.e., mappings from a subset of ε into ε). If ƒ is a function, we write δƒ and ρƒ for its domain and range respectively. The relation of inclusion is denoted by ⊂ and that of proper inclusion by ⊆.