#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e6 + 5;
const int mod = 1e9 + 7;
const int inf = 0x3f3f3f3f;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin >> n;
  int flg = 0, mx = 0, my = 0;
  for (int i = 1; i <= n; ++i) {
    char ch[2];
    int x, y;
    cin >> ch >> x >> y;
    if (ch[0] == '+') {
      if (!flg)
        flg = 1, mx = x, my = y;
      else {
        if (x <= mx && y <= my || x <= my && y <= mx)
          ;
        else if (x >= mx && y >= my || x >= my && y >= mx)
          mx = x, my = y;
        else {
          if (mx < my) swap(mx, my);
          if (x < y) swap(x, y);
          if (x > mx)
            mx = x;
          else
            my = y;
        }
      }
    } else {
      if (x >= mx && y >= my || x >= my && y >= mx)
        cout << "YES\n";
      else
        cout << "NO\n";
    }
  }
  return 0;
}
