# Some remarks on blueprints and ${\mathbb F}_1$-schemes

## TL;DR

This paper explores a new categorical framework for ${
m F}_1$-geometry using blueprints, establishing connections with classical schemes and expanding the category of ${
m F}_1$-schemes.

## Contribution

It introduces the category ${
m Sch}_{ ilde{
m B}}$ of schemes over blueprints, relating them to classical schemes and ${
m F}_1$-schemes, and merges existing ${
m F}_1$-theories.

## Key findings

- Defined the category ${
m Sch}_{ ilde{
m B}}$ for schemes over blueprints.
- Proved that each $ ilde{
m B}$-scheme relates to classical and ${
m F}_1$-schemes.
- Unified different ${
m F}_1$-geometries into a larger, more comprehensive category.

## Abstract

Over the past two decades several different approaches to defining a geometry over ${\mathbb F}_1$ have been proposed. In this paper, relying on To\"en and Vaqui\'e's formalism, we investigate a new category ${\mathsf{Sch}}_{\widetilde{\mathsf B}}$ of schemes admitting a Zariski cover by affine schemes relative to the category of blueprints introduced by Lorscheid. A blueprint, that may be thought of as a pair consisting of a monoid $M$ and a relation on the semiring $M \otimes_{{\mathbb F}_1} \mathbb N$, is a monoid object in a certain symmetric monoidal category $\mathsf B$, which is shown to be complete, cocomplete, and closed. We prove that every $\widetilde{\mathsf B}$-scheme $\Sigma$ can be associated, through adjunctions, with both a classical scheme $\Sigma_{\mathbb Z}$ and a scheme $\underline{\Sigma}$ over ${\mathbb F}_1$ in the sense of Deitmar, together with a natural transformation $\Lambda\colon \Sigma_{\mathbb Z}\to \underline{\Sigma}\otimes_{{\mathbb F}_1} {\mathbb Z}$. Furthermore, as an application, we show that the category of "${\mathbb F}_1$-schemes" defined by A. Connes and C. Consani can be naturally merged with that of $\widetilde{\mathsf B}$-schemes to obtain a larger category, whose objects we call "${\mathbb F}_1$-schemes with relations".