Volume 33 • Number 2 • 2010   • A Direct Approach to Co-Universal Algebras Associated to Directed Graphs Aidan Sims and Samuel B. G. Webster Abstract. We prove directly that if E is a directed graph in which every cycle has an entrance, then there exists a C*-algebra which is co-universal for Toeplitz-Cuntz-Krieger E-families. In particular, our proof does not invoke ideal-structure theory for graph algebras, nor does it involve use of the gauge action or its fixed point algebra. 2000 Mathematics Subject Classification: Primary: 46L05. Full text: PDF