#include <bits/stdc++.h>
using namespace std;
const int MAX = 200010;
const long long MOD = (int)1e9 + 7;
const int INF = 1e9;
const long long LLINF = 0x3f3f3f3f3f3f3f3f;
const long double EPS = 1e-8;
struct FT {
  vector<int> bit;
  int n;
  FT(int n) {
    this->n = n + 1;
    bit.assign(n + 1, 0);
  }
  int sum(int idx) {
    int ret = 0;
    for (idx++; idx > 0; idx -= idx & -idx) ret += bit[idx];
    return ret;
  }
  int sum(int l, int r) {
    if (l > r) return 0;
    return sum(r) - sum(l - 1);
  }
  void add(int idx, int delta) {
    for (idx++; idx < n; idx += idx & -idx) bit[idx] += delta;
  }
};
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  int q;
  cin >> q;
  int mx = 0, my = 0;
  while (q--) {
    char tipo;
    int x, y, w, h;
    cin >> tipo;
    if (tipo == '+') {
      cin >> x >> y;
      if (x > y) swap(x, y);
      mx = max(mx, x);
      my = max(my, y);
    } else {
      cin >> h >> w;
      if (h > w) swap(h, w);
      if (mx <= h and my <= w)
        cout << "YES" << '\n';
      else
        cout << "NO" << '\n';
    }
  }
  return 0;
}
