Brill-Noether theory of squarefree modules supported on a graph

Abstract

We investigate the analogy between squarefree Cohen-Macaulay modules supported on a graph and line bundles on a curve. We prove a Riemann-Roch theorem, we study the Jacobian and gonality of a graph, and we prove Clifford's theorem.Comment: Major revision, new author added, paper restructured, results correcte