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Problems in algebra inspired by universal algebraic geometry
B. I. Plotkin Hebrew University of Jerusalem
Abstract:
Let
$\Theta$ be a variety of algebras. In every variety
$\Theta$ and every algebra
$H$ from
$\Theta$ one can consider algebraic geometry in
$\Theta$ over
$H$. We also consider a special categorical invariant
$K_\Theta(H)$ of this geometry. The classical algebraic geometry deals with the variety
$\Theta=\mathrm{Com-}P$ of all associative and commutative algebras over the ground field of constants
$P$. An algebra
$H$ in this setting is an extension of the ground field
$P$. Geometry in groups is related to the varieties
$\mathrm{Grp}$ and
$\mathrm{Grp-}G$, where
$G$ is a group of constants. The case
$\mathrm{Grp-}F$, where
$F$ is a free group, is related to Tarski's problems devoted to logic of a free group. The described general insight on algebraic geometry in different varieties of algebras inspires some new problems in algebra and algebraic geometry. The problems of such kind determine, to a great extent, the content of universal algebraic geometry. For example, a general and natural problem is: When do algebras
$H_1$ and
$H_2$ have the same geometry? Or more specifically, what are the conditions on algebras from a given variety
$\Theta$ that provide the coincidence of their algebraic geometries? We consider two variants of coincidence: 1)
$K_\Theta(H_1)$ and
$K_\Theta(H_2)$ are isomorphic; 2) these categories are equivalent. This problem is closely connected with the following general algebraic problem. Let
$\Theta^0$ be the category of all algebras
$W=W(X)$ free in
$\Theta$, where
$X$ is finite. Consider the groups of automorphisms
$\operatorname{Aut}(\Theta^0)$ for different varieties
$\Theta$ and also the groups of autoequivalences of
$\Theta^0$. The problem is to describe these groups for different
$\Theta$.
UDC:
512.7