digraph pdf {
    entry [label="enter f()",style=filled];
	entry -> {while; D};
	while [label="while (O)",style=filled];
    C [style="bold,filled"]
    "if (P)" [style=filled]
    "if (Q)" [style=filled]
	while -> {"if (P)" C};
    break2 [style=filled]
    break1 [style=filled]
	"if (P)" -> {"if (Q)"};
	"if (Q)" -> {A break1};
	break1 -> B;
	break1 -> break2;
	break2 -> {C while};
	{rank=same; A break1 B break2}
	{rank=same; "if (Q)" C}
	{rank=same; while D}			
	{edge [style=invis];
		A -> break1 -> B -> break2;
	}
}