#include <bits/stdc++.h>
using namespace std;
void solve() {}
signed main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  long long n;
  cin >> n;
  long long r = 0, c = 0;
  for (long long i = 1; i <= n; i++) {
    char type;
    cin >> type;
    if (type == '+') {
      long long x, y;
      cin >> x >> y;
      if (x < y) swap(x, y);
      r = max(r, x);
      c = max(c, y);
    } else {
      long long x, y;
      cin >> x >> y;
      if (x < y) swap(x, y);
      if (r <= x and c <= y) {
        cout << "YES" << '\n';
      } else {
        cout << "NO" << '\n';
      }
    }
    if (false) cerr << r << " " << c << '\n';
  }
}
