#include <bits/stdc++.h>
using namespace std;
int n;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n;
  long long pq1 = -INT_MAX, pq2 = -INT_MAX;
  while (n--) {
    char c;
    long long x, y;
    cin >> c >> x >> y;
    if (c == '+') {
      pq1 = max(pq1, min(x, y));
      pq2 = max(pq2, max(x, y));
    } else if (c == '?') {
      if (pq1 > min(x, y)) {
        cout << "NO\n";
      } else if (pq2 > max(x, y)) {
        cout << "NO\n";
      } else {
        cout << "YES\n";
      }
    }
  }
  return 0;
}
