Изменения

digraph G { a [label="" pos="1,1.4!" style=filled fillcolor=black height=0.3 width=0.3]; b [label="" pos="0,0!" style=filled fillcolor=gray height=0.3 width=0.3]; c [label="" pos="2,0!" style=filled fillcolor=gray height=0.3 width=0.3]; c -> b [label="0" style=bold] b -> c [label="0" style=bold] }