indexLabelGraph(MixedGraph) -- relabel the vertices of a mixed graph according to their indices, indexed from 0

i1 : G= mixedGraph(graph{{a,b},{b,c}},digraph {{a,d},{c,e},{f,g}},bigraph {{d,e}})

o1 = MixedGraph{Bigraph => Bigraph{d => {e}}}
                                   e => {d}
                Digraph => Digraph{a => {d}}
                                   c => {e}
                                   d => {}
                                   e => {}
                                   f => {g}
                                   g => {}
                Graph => Graph{a => {b}   }
                               b => {a, c}
                               c => {b}

o1 : MixedGraph

i2 : indexLabelGraph G

o2 = MixedGraph{Bigraph => Bigraph{1 => {2}}}
                                   2 => {1}
                Digraph => Digraph{0 => {2}}
                                   1 => {}
                                   2 => {}
                                   3 => {4}
                                   4 => {}
                                   5 => {1}
                Graph => Graph{0 => {6}   }
                               5 => {6}
                               6 => {5, 0}

o2 : MixedGraph