The algebra of one-sided inverses of a polynomial algebra

TL;DR

This paper investigates the algebra $\\mS_n$, formed by adding one-sided inverses to polynomial algebra generators, revealing its structural properties, spectra, modules, and the lattice of its idempotent ideals, with connections to Dedekind numbers.

Contribution

It provides a detailed analysis of the algebra $\\mS_n$, including its dimensions, spectra, modules, and the explicit structure of its idempotent ideals, which was not previously known.

Findings

Krull dimension of $\\mS_n$ is $2n$

Weak and global dimensions of $\\mS_n$ are $n$

Number of idempotent ideals equals Dedekind number $\\gd_n$

Abstract

We study in detail the %Shrek algebra $\mS_n$ in the title which is an algebra obtained from a polynomial algebra $P_n$ in $n$ variables by adding commuting, {\em left} (but not two-sided) inverses of the canonical generators of $P_n$. The algebra $\mS_n$ is non-commutative and neither left nor right Noetherian but the set of its ideals satisfies the a.c.c., and the ideals {\em commute}. It is proved that the classical Krull dimension of $\mS_n$ is $2n$; but the weak and the global dimensions of $\mS_n$ are $n$. The prime and maximal spectra of $\mS_n$ are found, and the simple $\mS_n$-modules are classified. It is proved that the algebra $\mS_n$ is central, prime, and {\em catenary}. The set $\mI_n$ of idempotent ideals of $\mS_n$ is found explicitly. The set $\mI_n$ is a finite distributive lattice and the number of elements in the set $\mI_n$ is equal to the {\em Dedekind} number $\gd_n$.