#include <bits/stdc++.h>
using namespace std;
long long mypow(long long a, long long b) {
  if (b == 0) return 1;
  long long temp = mypow(a, b / 2);
  temp = (temp * temp) % 1000000007LL;
  if (b % 2 == 1) temp = (a * temp) % 1000000007LL;
  return temp;
}
int mygcd(int a, int b) {
  if (b == 0) return a;
  return mygcd(b, a % b);
}
int cntBits(long long a) {
  int ret = 0;
  while (a > 0) {
    ret++;
    a /= 2;
  }
  return ret;
}
int main() {
  ios::sync_with_stdio(0);
  int tt = 1, tcase;
  cin >> tt;
  int cd = 0, cm = 0;
  for (tcase = 1; tcase <= tt; tcase++) {
    char c;
    cin >> c;
    if (c == '+') {
      int x, y;
      cin >> x >> y;
      cd = max(cd, max(x, y));
      cm = max(cm, min(x, y));
    } else {
      int h, w;
      cin >> h >> w;
      if (max(h, w) >= cd && min(h, w) >= cm)
        cout << "YES\n";
      else
        cout << "NO\n";
    }
  }
  return 0;
}
