# File karel/world_maker.rb, line 141
    def remove(x, y, all)
      canvas = $window.canvas    
      avenue, street = scale(x, y)  
      # puts street.to_s + ' ' + avenue.to_s
      if(street < 1 or avenue < 1 or street > $window.number_of_streets() or avenue > $window.number_of_streets()) 
        return
      end
      if all
        $world.remove_all_beepers(street, avenue)
        canvas.update
      else
        if $world.beepers_at?(street, avenue)
          $world.remove_beeper(street, avenue) 
        else
          $world.place_beepers(street, avenue, -1)
        end      
      end

    end