Notice in the above graph that vertices \(a,c\) and \(d\) are kings in this graph. Vertex \(a\) is a king because \(a\rightarrow b\), \(a\rightarrow c\) and \(a\rightarrow c\rightarrow d.\) Vertex \(c\) is a king because \(c\rightarrow b\), \(c\rightarrow d\) and \(c\rightarrow d\rightarrow a.\) Vertex \(d\) is a king because \(d\rightarrow a\), \(d\rightarrow a\rightarrow b\), and \(d\rightarrow a\rightarrow c.\)