def delete(v)
      return unless include? v
      raise ArgumentError, "Item is protected and cannot be deleted" if protected? index(v)
      @list.delete v
    end
def delete(v)
      return unless include? v
      raise ArgumentError, "Item is protected and cannot be deleted" if protected? index(v)
      @list.delete v
    end
delete the item from the list
 @param [Any] v The item to be deleted.
 @raise [ArgumentError] if the item's index is protected by locking
 @return [Any] The item deleted