Maximum linearizations of lower sets in $\mathbb{N}^m$ with application to monomial ideals

TL;DR

This paper determines the maximum linearization types of bounded and unbounded lower sets in multi-dimensional natural numbers, providing bounds relevant to sequences of monomial ideals in polynomial rings.

Contribution

It computes the types of well partial orders of lower sets in N^m, extending understanding of their structure and applications to monomial ideal sequences.

Findings

Type of bounded lower sets in N^m is ω^{ω^{m-1}}.

Type of all lower sets in N^m is ω^{sum_{k=1}^{m} ω^{m-k} binom{m}{k-1}} + 1.

Provides bounds on sequences of monomial ideals in polynomial rings.

Abstract

We compute the type (maximum linearization) of the well partial order of bounded lower sets in $\mathbb{N}^m$, ordered under inclusion, and find it is $\omega^{\omega^{m-1}}$. Moreover we compute the type of the set of all lower sets in $\mathbb{N}^m$, a topic studied by Aschenbrenner and Pong, and find that it is equal to \[ \omega^{\sum_{k=1}^{m} \omega^{m-k}\binom{m}{k-1} }+ 1. \] As a consequence we deduce corresponding bounds on effectively given sequences of monomial ideals in $F[X,Y]$ where $F$ is a field.