Oh, its just a throw-away sentence about infinite sequences / sums, and the usage of lim x->infinity to solve that kind of problem.

The bulk of that section is about distributive property of summations, sum_A(foo) + sum_B(foo) == sum_AorB(foo) + sum_AandB(foo), and other such properties.

Its a primer on the mathematics of programming, which is almost entirely discrete mathematics. There's no integral or derivative in that section!