digraph {
    compound=true;

    a [style=dotted,shape=rectangle,label="{a}"];

    bc [style=dotted,shape=rectangle,label="{b,c}"];

    g [style=dotted,shape=rectangle,label="{g}"];

    h [style=dotted,shape=rectangle,label="{h}"];

    def [style=dotted,shape=rectangle,label="{d,e,f}"];

    a -> bc [style=dotted,shape=rectangle];
    a -> g [style=dotted,shape=rectangle];
    a -> h [style=dotted,shape=rectangle];

    h -> def [style=dotted,shape=rectangle];

    bc -> def [style=dotted,shape=rectangle];
}