#include <bits/stdc++.h>
int main() {
  std::ios_base::sync_with_stdio(false);
  std::cin.tie(NULL);
  int n, h, w, h_max = 0, w_max = 0;
  unsigned char c;
  std::cin >> n;
  for (int i = 0; i < n; ++i) {
    std::cin >> c >> h >> w;
    if (h > w) std::swap(h, w);
    if (c == '+') {
      h_max = std::max(h_max, h);
      w_max = std::max(w_max, w);
    } else if (h_max <= h && w_max <= w) {
      std::cout << "YES\n";
    } else {
      std::cout << "NO\n";
    }
  }
  return 0;
}
