A function call can have another function call as its argument, provided that this function has the same number and types of arguments in the correct order that the first function needs, e.g.: Suppose f1 needs 3 arguments f1(a, b, c int), and f2 returns 3 arguments: f2(a, b int) (int, int, int), then this can be a call to f1: f1(f2(a, b))
