This classification is due to the late Erik Sparre Andersen (1919-2003) [Andersen 89]. We consider sums of the form
T (c, n) = n∑
t(c, n, k), (5.1)
with n ∈ N0 the limit of summation, c ∈ C an argument-vector, and k ∈ N0 the summation variable. We can assume the lower limit to be equal to zero, because otherwise it is trivial to translate the formula to obtain this limit.