# nLab defining ideal of a topologizing subcategory

The notion of the defining sheaf of ideals of a closed subscheme inspires the notion of defining ideal of a topologizing subcategory $S$ of an abelian category $A$ as the endofunctor $\mathcal{I}=\mathcal{I}_S\in End(A)$ which is the subfunctor of identity $Id_A$ assigning to any $M\in A$ the intersection of kernels $Ker(f)$ of all morphisms $f: M\to N$ where $N\in Ob(S)$. One can show that if $T\subset S$ is an inclusion of topologizing subcategories, then $\mathcal{I}_{S}\subset \mathcal{I}_{T}$.

If $R$ is an associative unital ring and $J\subset R$ a left ideal in $R$. Let $T = [J]$ be the smallest coreflective subcategory of $A$ containing $R/J$. Then $\mathcal{I}_T(R)\subset R$ is a two-sided ideal, namely the maximal 2-sided ideal in $J$, which is explicitly, $(J:R) = \{r\in R\,|\, J r \subset J\}$. Moreover, $J_{T\circ T}$ where $T\circ T$ is the square under the Gabriel multiplication agrees with $(J:R)^2$.

• A. L. Rosenberg, Noncommutative algebraic geometry and representations of quantized algebras, MIA 330, Kluwer Academic Publishers Group, Dordrecht, 1995. xii+315 pp. ISBN: 0-7923-3575-9

• V. A. Lunts, A. L. Rosenberg, Differential calculus in noncommutative algebraic geometry I. D-calculus on noncommutative rings, MPI 1996-53 pdf

Created on May 12, 2011 16:34:06 by Zoran Škoda (148.6.183.21)