     topNodes = []
     nodes = []
     nodeMap = {}
+    links = []
 
     for topState in tree
         walk topState, (state, parent) ->

            else
                topNodes.push(node)

    r = 40

    cell = svg.selectAll('.cell')
        .data(nodes)

            .attr('width', (node) -> node.width)
            .attr('height', (node) -> node.height)

        link.attr('x1', (d) -> d.source.x)
            .attr('y1', (d) -> d.source.y)
            .attr('x2', (d) -> d.target.x)
            .attr('y2', (d) -> d.target.y)


doCollisions = (children) ->
    if children.length
