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std::____________<int> cont = {1, 2, 3};
// cont: {1, 2, 3}
auto it = cont.before_begin();
cont.insert_after(it, 0);
// cont: {0, 1, 2, 3}
auto it2 = cont.begin();
cont.emplace_after(it2, 99);
// cont: {0, 99, 1, 2, 3}
cont.erase_after(it2);
// cont: {0, 1, 2, 3}
std::____________<int> other = {7, 8, 9};
cont.splice_after(cont.before_begin(), other);
// cont: {7, 8, 9, 0, 1, 2, 3} , other: {}

std::forward_list<int> cont = {1, 2, 3};
// cont: {1, 2, 3}
auto it = cont.before_begin();
cont.insert_after(it, 0);
// cont: {0, 1, 2, 3}
auto it2 = cont.begin();
cont.emplace_after(it2, 99);
// cont: {0, 99, 1, 2, 3}
cont.erase_after(it2);
// cont: {0, 1, 2, 3}
std::forward_list<int> other = {7, 8, 9};
cont.splice_after(cont.before_begin(), other);
// cont: {7, 8, 9, 0, 1, 2, 3} , other: {}