0. Set of symbols
1. Alphabet
2. Deduction system
3. Theory
4. Zermelo-Fraenkel set theory
5. Set
6. Binary cartesian set product
7. Binary relation
8. Map
9. Function
10. Real function
11. Euclidean real function
12. Basic real function
13. Basic rational function
14. Basic integer function
15. Basic natural number function
Basic positive integer function
Formulation 0
A D18: Map $f : X \to Y$ is a basic positive integer function if and only if \begin{equation} Y \subseteq \{ 1, 2, 3, \ldots \} \end{equation}