Edge ideals of gapfree graphs with matching number $3$

Abstract

We prove that if $G$ is a gapfree graph with matching number $3$, then every power $I(G)^q$, $q\geq2$, of its edge ideal has linear quotients, and hence a linear resolution. Our approach combines graph reductions based on clique domination of gapfree graphs and matching number with operations preserving linear quotients. We reduce the problem to $26$ non-co-chordal graphs on at most seven vertices. A new preservation theorem for gapfree edge addition, together with known results on duplication and gapfree expansion, handles all but one of these graphs. For the remaining graph on seven vertices, we construct a linear quotients ordering for the square and extend it recursively to every higher power.