#include <iostream>
#include <list>
using namespace std;
 
int main() {
    list<int> numbers;
    for (int i = 0; i < 10; ++i) {
        numbers.push_back(i);
    }
 
    numbers.unique([](int a, int b){
        cout << a << ", " << b << endl;
        return a == b;
    });
    
    return 0;
}