digraph G {
	ranksep = .75; size = "7.5,7.5";
	rankdir="LR";

	node [shape=plaintext];

	{
		1970, 1972; 1985; 1989; 1992; 1995; 2007;
		"B";
	}

	{
		node [shape=circle];
		"Go";
	}

	{ rank = same; "1970"; "B"; }
	{ rank = same; "1972"; "C"; }
	{ rank = same; "1985"; "Squeak"; }
	{ rank = same; "1989"; "NewSqueak"; }
	{ rank = same; "1992"; "Alef"; }
	{ rank = same; "1995"; "Limbo"; }
	{ rank = same; "2007"; "Go"; }

	"B" -> "C" -> "Squeak" -> "NewSqueak" -> "Alef" -> "Limbo" -> "Go";
}