1. Cho, I.: Operators induced by graphs. Lett. Math. Phy 102(3), 323–369 (2012)
2. Cho, I.: Graph Groupoids and Partial Isometries. LAP Publisher, Saarbrücken (2009). ISBN 978- 3-8383-1397-9
3. Cho, I., Jorgensen, P.E.T.: Directed graphs, von Neumann Algebras, and Index. Alg. Rep. Theo. (2010). doi: 10.1007/s10468-010-9233-7
4. Cho, I., Jorgensen, P.E.T.: $C^{*}$ -dynamical systems induced by partial isometries. Adv. Appl. Math. Sci. 1(2), 21–59 (2010)
5. Cho, I.; Jorgensen, P.E.T.: Applications of automata and graphs: labeling-operators in Hilbert space I. ACTA Appl. Math. (2009). doi: 10.1063/1.3141524