如何从 boost::filter_iterator 获取原始迭代器？

std::vector<int> arr{1, -1, 1, 1, 1, 4, -1, 4, 4, 4, -1, 7, 8, -1};
auto begin = boost::make_filter_iterator<is_positive_number>(arr.begin(), arr.end());
auto end = boost::make_filter_iterator<is_positive_number>(arr.end(), arr.end());
auto lower = std::lower_bound(arr.begin(), arr.end(), i, [](const auto& val1, const auto& val2) {
        return val1 < val2;
    });
std::vector<int>::iterator iter = ??????(lower);