#include <bits/stdc++.h>
using namespace std;
int t, n, i, r, j, k, e, m, x, l, d, y, z, u, a1[4][4], b1[4][4], a2, b2, l1,
    r1;
int main() {
  char c2;
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for (j = 0; j < n; j++) {
    cin >> c2;
    if (c2 == '+') {
      cin >> l1 >> r1;
      if (l1 < r1) {
        swap(l1, r1);
      }
      l = max(l1, l);
      r = max(r1, r);
    } else {
      cin >> l1 >> r1;
      if (l1 < r1) {
        swap(l1, r1);
      }
      if (l1 < l || r1 < r) {
        cout << "NO";
      } else {
        cout << "YES";
      }
      cout << "\n";
    }
  }
}
