Upper triangular really should be interpreted as having only zero entries under the leading diagonal, which starts off at the upper left corner. Example[edit] M A M B M C M D M E M F M G M H M I M J M K M L M http://mensnoveltyunderwear66.blogzet.com/how-t-u-an-l-b-d-things-to-know-before-you-buy-10433557