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[10 pts] As in the previous problem we consider the m x n grid graph and assume m, n > 2. Recall that we showed in lecture that this graph has ma vertices and 2mn - m -n edges. This graph is clearly connected. Calculate D, the maximum number of edges that can be deleted from this graph without disconnecting it. Justify your answer. Then describe (informally) which D edges of the graph you can delete without disconnecting it (there is more than one such set of D edges). Solution