2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/67210We develop a theory of graph C*-algebras using path groupoids and inverse semigroups. Row finiteness is not assumed so that the theory applies to graphs for which there are vertices emitting a countably infinite set of edges. We show that the path groupoid is amenable, and give a groupoid proof of a recent theorem of Szymanski characterizing when a graph C*-algebra is simple.17 pagesOperator Algebras20M18; 22A22; 46L05text