#include <bits/stdc++.h>
#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast")
#pragma GCC target( \
    "sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#pragma GCC optimize("unroll-loops")
using namespace std;
const long long N = 1e6 + 5;
long long powmod(long long base, long long exp, long long mod) {
  long long res = 1LL;
  while (exp > 0) {
    if (exp & 1LL) res = (res * base) % mod;
    exp /= 2LL;
    base = (base * base) % mod;
  }
  return res % mod;
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long n;
  cin >> n;
  long long maxw = 0, maxh = 0, x, y;
  char some;
  for (long long i = 0; i < n; i++) {
    cin >> some >> x >> y;
    if (x > y) {
      swap(x, y);
    }
    if (some == '+') {
      maxh = max(y, maxh);
      maxw = max(x, maxw);
    } else {
      if (maxw > x || maxh > y) {
        cout << "NO" << '\n';
      } else {
        cout << "YES" << '\n';
      }
    }
  }
  return 0;
}
