# File karel/tk_robot_world.rb, line 278
  def get_display(startStreet, startAvenue, streetsTowardNorth, avenuesTowardEast) 
    xBound = 2 * streetsTowardNorth + 1
    yBound = 2 * avenuesTowardEast + 1
    
    display = []
     (0 ..xBound).each do |i|
      display<<[] # a row
      display<<[] # a row
       (avenuesTowardEast + 1).times do |j|
        display[2*i + 1]<< " . "
        display[2*i + 1]<< "   "
        display[2*i]<< "   "
        display[2*i]<< "   "
      end
    end
    #beepers
    @beepers.keys.each do |key|
      x, y = key[0], key[1]
      howMany = @beepers[key]
      if howMany > 9 
        cell = " * "
      elsif howMany < 0 
        cell = "inf"
      elsif howMany > 0
        cell = " " + howMany.to_s + " "
      else
        cell = " . "
      end
      x = 2 * (x - startStreet) + 1
      y = 2 * (y - startAvenue)
      display[x][y] = cell if visible(x, y, xBound, yBound)
    end
    #boundary walls
    bottom = 2 * (1 - startStreet)
    left = 2 * (1 - startAvenue)   
    yBound.times {|i| display[bottom][i] = "___"}  if bottom >= 0 and bottom < xBound 
    (xBound - 1).times {|i|  display[i+1][left-1] = display [i][left-1]= "|"} if left >= 1 and left < yBound 
    #eastwestwalls
    @east_west_walls.keys.each do |key|
      x, y = key[0], key[1]
      x = 2 * (x - startStreet) + 1
      y = 2 * (y - startAvenue)
      display[x + 1][y] = "___"  if  visible(x + 1, y, xBound, yBound) 
    end
    #northsouthwalls
    @north_south_walls.keys.each do |key|
      x, y = key[0], key[1]
      bottom = x
      x = 2 * (x - startStreet);
      y = 2 * (y - startAvenue) + 1;
      if visible(x + 1, y, xBound, yBound) 
        display[x + 1 ][y] = display[x][y] = " | "
        display[x][y] = "_|_" if bottom == 1 
      end
    end
    return display
  end