arXiv subjects
Publications and source records attributed to Colas Bardavid.
In this note, we give a simple necessary condition for the Zariski relative tangent space and the Grothendieck relative tangent space to be isomorphic.
In this paper, we give a geometrization and a generalization of a lemma of differential Galois theory. This geometrization, in addition of giving a nice insight on this result, offers us the occasion to investigate several points of differential algebra and differential algebraic geometry. We study the class of simple \D-schemes and prove that they all have a coarse space of leaves. Furthermore, instead of considering schemes endowed with one vector field, we consider the case of arbitrarilly large families of vector fields. This leads us to some developments in differential algebra, in particular to prove the existence of the trajectory in this setting but also to study simple \D-rings.
We define vector fields, leaves and trajectories for schemes. With these tools, we are able to give a geometrical interpretation and to generalize several results of differential Galois theory and constructions on differential schemes. We prove a theorem of extension of constant sections. Finally, as an application, we compare three classical sheaves defined over the differential spectrum.
We define, for any group $G$, finite approximations ; with this tool, we give a new presentation of the profinite completion $\hatπ : G \to \hat{G}$ of an abtract group $G$. We then prove the following theorem : if $k$ is a finite prime field and if $V$ is a $k$-vector space, then, there is a natural isomorphism between $\hat{V}$ (for the underlying additive group structure) and the additive group of the double-dual $V^{**}$. This theorem gives counter-examples concerning the iterated profinite completions of a group. These phenomena don't occur in the topological case.