digraph lattice2 {
    Top -> "NullableInstance(object)" -> "Instance(object)" -> "Instance(cls1)" -> Bottom;
    "NullableInstance(object)" -> "NullableInstance(cls1)" -> None -> Bottom;
    "NullableInstance(cls1)" -> "Instance(cls1)";

    "Instance(object)" -> "Instance(cls2)" -> Bottom;
    "NullableInstance(object)" -> "NullableInstance(cls2)" -> "Instance(cls2)";
    "NullableInstance(cls2)" -> None;
}
