Computing K-theory and Ext for graph C*-algebras

摘要

K-theory and Ext are computed for the C*-algebra C*(E) of any countabledirected graph E. The results generalize the K-theory computations of Raeburnand Szymanski and the Ext computations of Tomforde for row-finite graphs. As aconsequence, it is shown that if A is a countable {0,1} matrix and E_A is thegraph obtained by viewing A as a vertex matrix, then C*(E_A) is not necessarilyMorita equivalent to the Exel-Laca algebra O_A.