 The starting point for these number theorists is the solution of algebraic equations, especially their solution in terms of integers. A famous example is Fermat’s Last Theorem, which concerns the (non-)solubility of the equation \(x^n + y^n = z^n\) by integers, for different exponents \(n\). The approach to the problem developed by Gauss, clarified and refined by Dirichlet, and pushed further by Kummer involves considering extensions of the (field of) rational numbers, as well as of the (ring of) “integers” contained in such extensions. Thus, Gauss studied the “Gaussian integers” (\(a + bi\), where \(a\) and \(b\) are regular integers and \(i = \sqrt{-1}\)) within the field of all complex numbers; Kummer considered more complicated “cyclotomic integers” in corresponding cyclotomic number fields (Edwards 1977, Stillwell 2000, Gray 2018).