subgraph_c1.dot

digraph {
    rankdir=LR

    a[label="α"]
    b[label="β"]
    c[label="γ"]
    d[label="δ"]
    e[label="ε"]
    f[label="ζ"]

    subgraph cluster1 {
        rank = same;
        style = "filled";
        fillcolor = "#80ff80";
        a;
        a1;
        a2;
    }

    a -> b;
    b -> c;
    c -> d;
    d -> e;
    e -> f;
    f -> a;

    b -> a;
    c -> b;
    d -> c;
    e -> d;
    f -> e;
    a -> f;

    a -> a1;
    a -> a2;
    b -> b1;
    b -> b2;
    c -> c1;
    c -> c2;
    d -> d1;
    d -> d2;
    e -> e1;
    e -> e2;
    f -> f1;
    f -> f2;
}