# File karel/robot_world.rb, line 64
  def remove_beeper(street, avenue)
    key = [street, avenue]   
    return if @Beepers[key] == Robota::INFINITY
    if @Beepers[key] > 0
      @Beepers[key] -= 1
    else
      raise NoBeepers, "(#{street}, #{avenue})"
    end
    nil
  end