The geometry of blueprints. Part I: Algebraic background and scheme theory

In this paper, we introduce the category of blueprints, which is a category of algebraic objects that include both commutative (semi)rings and commutative monoids. This generalization allows a simultaneous treatment of ideals resp.
congruences for rings and monoids and leads to a common scheme theory. In particular, it bridges the gap between usual schemes and ${\mathbb{F}}_1$-schemes (after Kato, Deitmar and Connes-Consani). Beside this unification, the category of blueprints contains new interesting objects as “improved” cyclotomic field extensions ${\mathbb{F}}_{1^n}$ of ${\mathbb{F}}_1$ and “archimedean valuation rings”. It also yields a notion of semiring schemes. This first paper lays the foundation for subsequent projects, which are devoted to the following problems: Tits’ idea of Chevalley groups over ${\mathbb{F}}_1$, congruence schemes, sheaf cohomology, $K$-theory and a unified view on analytic geometry over ${\mathbb{F}}_1$, adic spaces (after Huber), analytic spaces (after Berkovich) and tropical geometry.