#include <bits/stdc++.h>
using namespace std;
using i64 = int64_t;
using vi = vector<i64>;
using vvi = vector<vi>;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  int q;
  cin >> q;
  i64 naxh = 0, naxw = 0;
  while (q--) {
    char c;
    cin >> c;
    if (c == '+') {
      i64 a, b;
      cin >> a >> b;
      naxh = max(naxh, min(a, b));
      naxw = max(naxw, max(a, b));
    } else {
      i64 a, b;
      cin >> a >> b;
      i64 h = min(a, b), w = max(a, b);
      cout << (naxh <= h && naxw <= w ? "YES" : "NO") << '\n';
    }
  }
}
