Mathematics is simple—or more precisely: dual. Essentially, one deals with only two types of objects, namely sets and mappings. In the first section, the corresponding terms are introduced in a rather informal way and some basic properties are proven. Subsequently, general structures of mathematics such as groups, rings, and fields are discussed, with arithmetic aspects initially being in the foreground. This essentially sets the rules of the game. Classical formulas such as the geometric sum formula and the binomial formula are formulated in a comparatively general framework. The extension to an order structure represents the transition to analysis, where primarily estimates and approximations are at the center of the investigations.