1. The problem statement, all variables and given/known data Hey guys, I'm just going through a Laurent series example and I'm having trouble understanding how they switched the index on a summation from n=0 to n=1 and then switched the argument from z^(-n-1) to z^n as well as changing the upper limit to -infinity. If anyone could shed some light on that for me I would really appreciate it. 2. Relevant equations http://imgur.com/0PkgLim 3. The attempt at a solution I thought that if you changed the index to n=1 then the power on z should just move up one erasing the ^(-1) and i'm not sure how switching the limit to negative infinity changes anything. Thanks for any help.