A1 = function(id)
	-- like A, but translate a single node in Nodes to Surface
	-- this only works because Nodes is a flat array; we don't support row/col types here yet
	-- delete previously added shapes for this node:
	for i=#Surface,1,-1 do
		local x = Surface[i]
		if x.id == id or (x.keys and table.find(x.keys, id)) then
			table.remove(Surface, i)
		end
	end
	-- translate Nodes to Surface
	local node = Nodes[id]
	compute_layout(node, node.x,node.y, Surface)
	for _,d in ipairs(node.outgoing_edges) do
		compute_layout_for_edge(id, d)
	end
	for _,s in ipairs(node.incoming_edges) do
		compute_layout_for_edge(s, id)
	end
	-- continue the pipeline
	B()
end