Relative graphs and pullbacks of relative Toeplitz graph algebras

Abstract

In this note we generalize a result from a recent paper of Hajac, Reznikoff and Tobolski ([5]). In that paper they give conditions they call admissibility on a pushout diagram in the category of directed graphs implying that the C * -algebras of the graphs form a pullback diagram. We consider a larger category of relative graphs that correspond to relative Toeplitz graph algebras. In this setting we give necessary and sufficient conditions on the pushout to get a pullback of C * -algebras.