Function problem_18

examples/99_problems.cpp:157–160

P18 (**) Extract a slice from a list.

// P18 (**) Extract a slice from a list.
void problem_18()
{
    print_result(get_segment(2, 4 + 1, xs));
}

// P19 (**) Rotate a list N places to the left.
void problem_19()