1. The problem statement, all variables and given/known data Could anyone please help me understand this notation? What is "it" under the variables? Is it some kind of sequence notation with 2 dimensions, or sequence notation which has the sequence member number multiplied by some other variable? What is this? Also, what could 0 over z mean, other than 0 exponent? 2. Relevant equations 3. The attempt at a solution Tried Google search without help.