 The fragment of the mathematical universe that emerges is relatively uncontroversial and both Platonists and constructivists might agree on its basic merits. On the basis of Peano’s axioms we can define more complex functions like addition and multiplication which are closed on \(\mathbb{N}\) and the inverse functions, subtraction and division, which are not closed and lead to the set of whole numbers \(\mathbb{Z}\) and the rational numbers \(\mathbb{Q}\). 