Countable vector spaces with recursive operations Part I1
J. C. E. Dekker · Journal of Symbolic Logic · 1969
We use the word “number” for “nonnegative integer” and “set” for collection of numbers. The set of all numbers is denoted by ε and the empty set by ο. We write ⊂ for the relation of inclusion and ⊆ for that of proper inclusion. If ƒ is a function from a subset of ε into ε, its domain and range are denoted by δƒ and ρƒ respectively. For any collection Γ of entities, card Γ or card (Γ) stands for the cardinality of Γ. The cardinality of the continuum is denoted by c.