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(A) This is an example of a bidirected graph. By convention, we draw edges that are positive(negative) incident to a vertex using an out(in) arrow at that vertex. The sequence W, A, X, B, Y, C, Y, B, X, D, Z is a walk, while W, A, X, D, Z is not. (B) The corresponding edge incidence matrix, with the zero entries ommited. (C) This is the associated monotonized directed graph.
