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## Main Question or Discussion Point

For any integer valued RV X Summation n=0 to infinity of s^n P(X=<n) = (1-s)^-1 * Summation k=0 to infinity of P(x=k)s^k

Why does Sum k=0 to infinity P(x=k)s^k = sum n=0 to infinity of P(X=< n)

Why does Sum k=0 to infinity P(x=k)s^k = sum n=0 to infinity of P(X=< n)