For a row-finite graph G with no sinks and in which every loop has an exit,we construct an isomorphism between Ext(C*(G)) and coker(A-I), where A is thevertex matrix of G. If c is the class in Ext(C*(G)) associated to a graphobtained by attaching a sink to G, then this isomorphism maps c to the class ofa vector which describes how the sink was added. We conclude with anapplication in which we use this isomorphism to produce an example of arow-finite transitive graph with no sinks whose associated C*-algebra is notsemiprojective.
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