template<class T> class Set {
	list<T> elems;
public:
	Set() {}
	Set(T val)
	{
		elems = list<T>();
		elems.push_back(val);
	}
	Set(const Set<T>& s) {
		elems = list<T>(s.elems);
	}
	bool isEmpty() const
	{
		return elems.empty();
	}
	Set<T> Union(const Set<T>& r) const {
		Set<T> res(*this);
		for each(T val in r.elems) {
			if (!contains(val))
				res.elems.push_front(val);
		}
		return res;
	}
	Set<T> intersection(const Set<T>& r) const {
		Set<T> res;
		for each (T val in elems) {
			if (r.contains(val))
				res.elems.push_front(val);
		}
		return res;
	}
	Set<T> subtract(const Set<T>& r) const {
		Set<T> res;
		for each (T val in elems) {
			if (!r.contains(val))
				res.elems.push_front(val);
		}
		return res;
	}
	bool contains(const T val) const {
		for each (T val2 in elems) {
			if (val == val2)
				return true;
		}
		return false;
	}
	bool contains(const Set<T> r) const {
		for each(T val in r) {
			if (!contains(val))
				return false;
		}
		return true;
	}
	bool insert(const T val) {
		if (!contains(val)) {
			elems.push_front(val);
			return true;
		} else {
			return false;
		}
	}
	bool erase(const T val) {
		for (auto it = elems.begin(); it != elems.end(); it++) {
			if (*it == val) {
				elems.erase(it);
				return true;
			}
		}
		return false;
	}
};