Need Help On Implementing The Intersection Function.

#include <iostream>
using namespace std;

template<class T>
class OLL
{
private:struct NODE
		{
			T info;
			NODE *next;
		};
		NODE *list;
public: OLL()
		{
			list = NULL;
		}
		void insert (T x)
		{
			NODE *p = list, *q = list, *r;
			//create new node
			r = new (NODE); r -> info = x;
			r -> next = NULL;

			//find the insertion place
			while (p != NULL && p -> info < x)
			{
				q = p; p = p -> next;
			}
			if (p == list) // x is the first info
			{
				list = r; r -> next = p;
			}
			else if (p == NULL) // x is the last info
			{
				q -> next = r;
			}
			else //x is neither first nor last info
			{
				r -> next = p; q -> next = r;
			}
		}
		void display ()
		{
			NODE *p = list;
			while (p != NULL)
			{
				cout<<p->info<<" --> ";
				p = p -> next;
			}
			cout << "NULL\n";
		}
		void display (OLL <T> Tset)
		{
			while (Tset.list != NULL)
			{
				cout<<Tset.list -> info<<" --> ";
				Tset.list = Tset.list -> next;
			}
			cout<<"NULL\n";
		}
		void FindAUB(OLL setA, OLL setB, OLL &U)
		{
			NODE *a = setA.list;
			NODE *b = setB.list;
			while (a != NULL && b != NULL)
			{
				if (a->info < b->info)
				{
					U.insert(a->info);
					a = a->next;
				}
				else if (b->info < a->info)
				{
					U.insert(b->info);
					b = b->next;
				}
				else
				{
					U.insert(a->info);
					a = a->next;
					b = b->next;
				}
			}
			while (a != NULL)
			{
				U.insert(a->info);
				a = a->next;
			}
			while (b != NULL)
			{
				U.insert(b->info);
				b = b->next;
			}
		}
};
int main()
{
	//create set of integers
	OLL <int> setA, setB, setAUB;

	//insert set A
	int A[4] = {3, 9, 6, 8};
	int B[7] = {17, 19, 2, 6, 4, 1, 3};

	//set A
	for (int i=0; i<4; ++i)
	{
		setA.insert(A[i]);
	}
	setA.display();

	//set B
	for (int i=0; i<7; ++i)
	{
		setB.insert(B[i]);
	}
	setB.display();

	//set AUB
	setA.FindAUB(setA, setB, setAUB);
	setAUB.display();

	//Terminate Program
	system("pause");
	return 0;
}