graph G { node [shape=circle, texmode=math, fixedsize=True, width="0.4", style="filled, shadow=true", color="blue"]; edge [style="linecolor=green, showpoints=true,dotstyle=triangle"]; a_1-- a_2 -- a_3 -- a_1; node [shape=box, style="shadow=true", label=""]; edge [style="linecolor=red, shadow=true"]; b_1 -- b_2 -- a_2; }