# File karel/world_maker.rb, line 188
    def remove(x, y, all)
       canvas = $window.canvas      
      avenue, street = scale(x, y)  
      if(street < 1 or avenue < 1 or street > $window.number_of_streets() or avenue > $window.number_of_streets()) 
        return
      end
     $world.remove_wall_north_of(street, avenue)     
    end