Erasing element from List

Question

/*Erased the address of element in first iteration but in next iteration list is trying to erase the same address of element. For example :- I tried to erase duplicate element from list So Initially my list looked like 1,2,3,4,2,3,5,6 So in first iteration i deleted 2 if the address of element is not same. In cout it's printing 1,3,4,5,6 but for next iteration i m getting segfault. When i checked in debug i found in next iteration again it is trying to delte 2 which was already deletedd. As per my understanding list should get updated after erase then why in next iteration it's getting element 2 ?. */

int main()
{
        vector<pair<int,int>> v1 = {make_pair(1,2),make_pair(3,4)};
        vector<pair<int,int>> v2 = {make_pair(2,3),make_pair(5,6)};
        list<int>v3;
        list<int>::iterator it;
        list<int>::iterator itip;
        vector<pair<int,int>> v4;
        int count = 0;

        for (auto &i :v1)
        {
                v3.push_back(i.first);
                v3.push_back(i.second);
        }
        for (auto &i :v2)
        {
                v3.push_back(i.first);
                v3.push_back(i.second);
        }
        for (itip=v3.begin(); itip != v3.end(); itip++ )
        {
                for (it = v3.begin() ; it != v3.end(); it++ )
                {
                        if (*itip == *it)
                        {
                                if (itip != it )
                                {
                                   v3.erase(itip);
                                   v3.erase(it);
                                   cout<<"List After erased"<<endl;
                                   for (auto &i : v3)
                                   {
                                        cout<<i<<"\t";
                                   }
                                   cout<<"List After erased"<<endl;
                                   break;
                                }
                        }
                }
        }
        cout<<endl;
        for (auto &i : v3)
        {
                cout<<i<<"\t";
        }

        return 0;
}