The structure of claw-free binary matroids

TL;DR

This paper characterizes the structure of claw-free binary matroids, showing they are either from specific basic classes or built from them via a join operation, providing a complete decomposition theorem.

Contribution

It provides the first complete structural decomposition theorem for claw-free binary matroids, identifying basic classes and a construction method.

Findings

Claw-free matroids belong to three basic classes or are constructed from them.

The decomposition theorem fully characterizes the structure of all claw-free binary matroids.

The paper introduces a join operation to build complex claw-free matroids from basic classes.

Abstract

A simple binary matroid is called claw-free if none of its rank-3 flats are independent sets. These objects can be equivalently defined as the sets $E$ of points in $\mathrm{PG}(n-1,2)$ for which $|E \cap P|$ is not a basis of $P$ for any plane $P$, or as the subsets $X$ of $\mathbb{F}_2^n$ containing no linearly independent triple $x,y,z$ for which $x+y,y+z,x+z,x+y+z \notin X$. We prove a decomposition theorem that exactly determines the structure of all claw-free matroids. The theorem states that claw-free matroids either belong to one of three particular basic classes of claw-free matroids, or can be constructed from these basic classes using a certain 'join' operation.