Graph algebras, Exel-Laca algebras, and ultragraph algebras coincide up to Morita equivalence

Abstract

We prove that the classes of graph algebras, Exel-Laca algebras, and ultra- graph algebras coincide up to Morita equivalence. This result answers the long-standing open question of whether every Exel-Laca algebra is Morita equivalent to a graph algebra. Given an ultragraph G we construct a directed graph E such that C � (G) is isomorphic to a full corner of C � (E). As applications, we characterize real rank zero for ultragraph algebras and describe quotients of ultragraph algebras by gauge-invariant ideals.