auto num_it = nums.begin(), num_itend = nums.end();
auto den_it = dens.begin(), den_itend = dens.end();
//std::clog << " num = " << *num_it << ", den = " << *den_it << std::endl;
auto num_it = nums.begin(), num_itend = nums.end();
auto den_it = dens.begin(), den_itend = dens.end();
//std::clog << " num = " << *num_it << ", den = " << *den_it << std::endl;