# The Lefschetz question for ideals generated by powers of linear forms in few variables

## TL;DR

This paper investigates the Lefschetz property for ideals generated by powers of linear forms in few variables, establishing new results for maximal rank conditions and Lefschetz properties in low-dimensional polynomial rings.

## Contribution

It extends known Lefschetz results to higher powers of linear forms and provides a complete characterization for when multiplication by these powers has maximal rank.

## Key findings

- Multiplication by L^2 has maximal rank in three variables for general linear forms.
- Complete description of maximal rank conditions for multiplication by L^3.
- Results on Strong and Weak Lefschetz Properties for specific ideals in three and four variables.

## Abstract

The Lefschetz question asks if multiplication by a power of a general linear form, $L$, on a graded algebra has maximal rank (in every degree). We consider a quotient by an ideal that is generated by powers of linear forms. Then the Lefschetz question is, for example, related to the problem whether a set of fat points imposes the expected number of conditions on a linear system of hypersurfaces of fixed degree. Our starting point is a result that relates Lefschetz properties in different rings. It suggests to use induction on the number of variables, $n$. If $n = 3$, then it is known that multiplication by $L$ always has maximal rank. We show that the same is true for multiplication by $L^2$ if all linear forms are general. Furthermore, we give a complete description of when multiplication by $L^3$ has maximal rank (and its failure when it does not). As a consequence, for such ideals that contain a quadratic or cubic generator, we establish results on the so-called Strong Lefschetz Property for ideals in $n=3$ variables, and the Weak Lefschetz Property for ideals in $n=4$ variables.