>[!abstract] >A mnemonic for the nesting of number sets: >- $\mathbb{N}$ for natural numbers (positive integers); >- $\mathbb{Z}$ for all integers, positive and negative (Z stands for *Zahl* or integer in German); >- $\mathbb{Q}$ for rational numbers (i.e., those that can be expressed as a ratio; Q stands for quotient); >- $\mathbb{R}$ for real numbers; >- $\mathbb{C}$ for complex numbers (i.e., those with an imaginary part).