Nested default procs

gistfile1.rb

intersections = Hash.new do |h, k|
                  # k = segment type 1
                  h[k] = Hash.new do |h, k|
                           # k = segment value 1
                           h[k] = Hash.new do |h, k|
                                    # k = segment type 2
                                    h[k] = {}
                                  end
                         end
                end