struct Node
{
	T key;
	Node *previous;
	Node *next;

	Node() : key(T()), previous(NULL), next(NULL) {}
	Node(T k) : key(k), previous(NULL), next(NULL) {}
	Node(T k, Node *prev, Node *nxt) : key(T()), previous(prev), next(nxt) {}
	Node(Node *t) : key(t->key), previous(t->previos), next(t->next) {}
};