digraph G {

subgraph cluster_0 {
S4
S0
}

subgraph cluster_1 {
S3
S1
}

subgraph cluster_3 {
H5
H0
H6
}

subgraph cluster_5 {
H4
H3
H1
}

S2
H2

S0 -> S3 [constraint=false]
S4 -> S0
S3 -> S1
S0 -> S2 [constraint=false]
H5 -> H1 [label=a,constraint=false]
H6 -> H5
H4 -> H3
H1 -> H4
H0 -> H6
H5 -> H2 [constraint=false]
S4 -> H0 [constraint=false]
S3 -> H1 [constraint=false]
S2 -> H2 [constraint=false]
S1 -> H4 [label=b,constraint=false]
S1 -> H3 [constraint=false]
S0 -> H6 [constraint=false]
S0

 -> H5 [constraint=false]
}


