def can_not(*args)
      args.last.is_a?(Hash) ? args.last[:restriction]= true : args << {:restriction => true}
      add_permission(@restrictions, *args)
    end
def can_not(*args)
      args.last.is_a?(Hash) ? args.last[:restriction]= true : args << {:restriction => true}
      add_permission(@restrictions, *args)
    end
Define a restriction ( a negative permission ) for the current role.

 Can only be called within a role block.

 @example
 can_not :delete, Post

 @see #can Argument details and further examples