#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n, x = 0, y = 0, xl = 0, yl = 0;
  char ch;
  cin >> n;
  while (n--) {
    cin >> ch >> x >> y;
    if (ch == '+') {
      if (x >= y) {
        if (x >= xl || y >= yl) {
          xl = xl > x ? xl : x;
          yl = yl > y ? yl : y;
        }
      } else {
        if (x >= yl || y >= xl) {
          yl = yl > x ? yl : x;
          xl = xl > y ? xl : y;
        }
      }
    }
    if (ch == '?') {
      if (xl <= x && yl <= y)
        cout << "YES\n";
      else if (xl <= y && yl <= x)
        cout << "YES\n";
      else
        cout << "NO\n";
    }
  }
  return 0;
}
