Пытаюсь скопировать обьекты list в set.Выдаёт ошибку

#include <iostream>
#include <set>
#include <list>
#include <time.h>
#include <algorithm>


using namespace std;

class point
{
private:
    int x;
    int y;
public:
    point()
    {
        x = 0;
        y = 0;
    }
    point(int a, int b)
    {
        x = a;
        y = b;
    }
    void operator =(point& a)
    {
        this->x = a.x;
        this->y = a.y;
    }
    const bool operator <(point&  a) const
    {
        if ((this->x +this->y)< (a.x + a.y))
        {
            return true;
        }
        else
        {
            return false;
        }
    }
    bool operator >(point& a)const
    {
        if ((this->x + this->y) > (a.x + a.y))
        {
            return true;
        }
        else
        {
            return false;
        }
    }
    bool operator ==(point& a)const
    {
        if ((this->x == a.x)&&(this->y == a.y))
        {
            return true;
        }
        else
        {
            return false;
        }
    }
    void show()
    {
        cout << '(' << x << "," << y << ") ";
    }
    int GetX() { return x; };
    int GetY() { return y; };
};


//template<typename T1>
auto copy_if(list<point> &a,set<point> &b)
{
    int current_x;
    int current_y;
    cout << "x = "; cin >> current_x;
    cout << "y = "; cin >> current_y;
    point current(current_x, current_y);
    for (auto &x : a)
    {
        if (x < current)
        {
            b.insert(x);

        }
    }
    return b.begin();

}





int main()
{
    srand(time(NULL));
    int N;
    int current_x;
    int current_y;
    cout << "N = "; cin >> N;
    list<point> l;
    for (int i = 0; i < N; i++)
    {
        l.push_back(point(rand() % 100, rand() % 100));
    }
    l.sort();
    for (auto& i : l)
    {
        i.show();
    }
    cout << endl;
    cout << "x = "; cin >> current_x;
    cout << "y = "; cin >> current_y;
    point current(current_x, current_y);
    auto a = find_if(l.begin(), l.end(), [&](point& a){return (a == current);});
    if (a == l.end())
    {

    }
    else
    {
        (*a).show();
    }
    set<point> s;
    /*cout << "x = "; cin >> current_x;
    cout << "y = "; cin >> current_y;
    point current1(current_x, current_y);
    remove_copy_if(l.begin(), l.end(), s.begin(),[&](point& c) {return (c > current1);});*/
    copy_if(l, s);
    for (auto& i : s)
    {

    }


}

Помогите пожалуйста, не понимаю, он выдаёт ошибку что не найдет оператор"<"хотя я перегрузил все операторы