A= [aij] n x n lower triangular matrix
B= [bij] n x n lower triangular matrix
C= [cij] = AB
Proof cij= 0 for i < j or lower diagonal
cij= [ ai1b1j + ai2b2j + ...+ai(j-1)b(j-1)j ] + [ aijbjj +....+ainbnj ]
I am a little confuse of what they are trying to show within the 2 brackets.