Bipartite Diametrical Graphs of Diameter 4 and Extreme Orders

<table>Two nonisomorphic <svg height="11.75" id="M333" style="vertical-align:-0.23206pt" version="1.1" viewbox="0 0 8.2875004 11.75" width="8.2875004" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<g transform="matrix(.017,-0,0,-.017,.062,11.4)"><path d="M457 488l-30 -3q-17 148 -131 148q-53 0 -84.5 -34.5t-31.5 -82.5q0 -42 25.5 -72t74.5 -62l33 -22q63 -42 95 -85t32 -102q0 -84 -67 -137t-163 -53q-58 0 -113 22t-70 43l-4 152l27 4q4 -32 15 -62.5t31 -59.5t53.5 -47t76.5 -18q56 0 92 35t36 96q0 39 -25 70t-78 68
l-31 22q-32 23 -53.5 41.5t-45 57t-23.5 77.5q0 82 58 132.5t156 50.5q46 0 101 -17l18.5 -6t17 -6t8.5 -3q-4 -55 0 -147z" id="x1D446"></path></g>
</svg>-graphs with minimum <svg height="14.85" id="M334" style="vertical-align:-2.22495pt" version="1.1" viewbox="0 0 26.3375 14.85" width="26.3375" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<g transform="matrix(.017,-0,0,-.017,.062,12.012)"><path d="M162 -163h-61v866h61v-866z" id="x7C"></path></g><g transform="matrix(.017,-0,0,-.017,4.533,12.012)"><path d="M1004 650l-6 -29q-54 -6 -71 -19.5t-51 -74.5l-271 -539h-33l-98 506h-3l-258 -506h-30l-78 532q-10 67 -21.5 80t-66.5 21l6 29h241l-8 -29l-26 -5q-34 -6 -41 -16t-3 -47l59 -425h4l251 510h31l102 -510h2q150 299 198 423q14 40 8.5 48.5t-47.5 16.5l-28 5l7 29h231z
" id="x1D44A"></path></g><g transform="matrix(.017,-0,0,-.017,21.804,12.012)"><path d="M162 -163h-61v866h61v-866z" id="x7C"></path></g>
</svg>.
Any two vertices of <svg height="11.175" id="M335" style="vertical-align:-0.0pt" version="1.1" viewbox="0 0 15.0375 11.175" width="15.0375" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<g transform="matrix(.017,-0,0,-.017,.062,11.113)"><path d="M865 650q-1 -4 -4 -14t-4 -14q-62 -5 -77 -19.5t-29 -82.5l-74 -394q-12 -61 -0.5 -77t75.5 -21l-6 -28h-273l8 28q64 5 82 21t29 76l36 198h-380l-37 -197q-11 -64 0.5 -78.5t79.5 -19.5l-6 -28h-268l6 28q60 6 75.5 21.5t26.5 76.5l75 394q13 66 2 81.5t-77 20.5l8 28
h263l-6 -28q-58 -5 -75.5 -21t-30.5 -81l-26 -153h377l29 153q12 67 2 81t-74 21l5 28h268z" id="x1D43B"></path></g>
</svg> at distance 2 from each other have exactly 2
common neighbors.</table>

International Journal of Mathematics and Mathematical Sciences

Bipartite Diametrical Graphs of Diameter 4 and Extreme Orders

Figure 1