}
	indexOf := make([]int, f.NumBlocks())
	for i, b := range f.Blocks {
		indexOf[b.ID] = i
	}
	layoutDrawn := make([]bool, f.NumBlocks())

	ponums := make([]int32, f.NumBlocks())
	_ = postorderWithNumbering(f, ponums)
	isBackEdge := func(from, to ID) bool {
		return ponums[from] <= ponums[to]
	}