#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 100;
const int INF = 0x3f3f3f3f;
const int mod = 998244353;
int main() {
  int n;
  cin >> n;
  char op[2];
  int x, y, h, w;
  int l, r;
  l = 0;
  r = 0;
  while (n--) {
    scanf("%s", op);
    if (op[0] == '+') {
      scanf("%d%d", &x, &y);
      l = max(l, min(x, y));
      r = max(r, max(x, y));
    } else {
      scanf("%d%d", &h, &w);
      if (l <= min(h, w) && r <= max(h, w))
        cout << "YES" << '\n';
      else
        cout << "NO" << '\n';
    }
  }
  return 0;
}
