Moreira's Theorem for Image Partition Regular Matrices

Abstract

The famous Hindman conjecture says that for any finite coloring of natural numbers, there exists a monochromatic copy of the form $\{x,x+y,xy\}.$ In a celebrated article, Moreira gave a partial answer to this conjecture by showing that every finite coloring of the natural numbers contains a monochromatic configuration of the form $\{x,x+y,xy\}$. In this article we prove matrix versions (both finite and infinite) of Moreira's theorem. A matrix $A$ is said to be an image partition regular matrix if for any finite coloring of naturals, there exists a monochromatic image of $A,$ i.e. there exists a vector $\vec{X}$ such that all the entries of $A\vec{X}$ are monochromatic. From a recent paper of Bowen, one can derive the finite matrix version of the Moreira theorem: if $A$ and $B$ are two finite image partition regular matrices of the same order, then under any finite coloring of $\mathbb{N}$, there exist vectors $\vec{X}$ and $\vec{Y}$ such that all entries in the union of $A\vec{X},A\vec{X}+B\vec{Y},A\vec{X}\cdot B\vec{Y}$ are monochromatic, where $A\vec{X}\cdot B\vec{Y}$ denote the vector each of its entries are pointwise multiplication of the coordinates of $A\vec{X}\text{ and }B\vec{Y}$. In this article, we give a short combinatorial proof of this result, and then we extend it to infinite image partition regular matrices.