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The identification of diametrical vertices in the d-dimensional hypercube (d ? 3) leads to a (0، نويسنده , , 2)-graph of degree d on 2d?1 vertices and of diameter ? d2 ? namely the extended odd graph (or Laborde-Mulder graph) for odd values of d، نويسنده , , and the half-cube for even values of d. In this paper we prove that the diameter of a (0، نويسنده , , 2)-graph of degree d on 2d?1 vertices is at least ? d2 ?، نويسنده , , and when d is odd the equality holds if and only if the graph is a Laborde-Mulder graph.، نويسنده ,
