#include <bits/stdc++.h>
using namespace std;
template <class T>
T cdiv(T num, T den) {
  return (num / den) + (num % den > 0);
}
template <typename TH>
void _dbg(const char* sdbg, TH h) {
  cerr << sdbg << "=" << h << "\n";
}
template <typename TH, typename... TA>
void _dbg(const char* sdbg, TH h, TA... t) {
  while (*sdbg != ',') cerr << *sdbg++;
  cerr << "=" << h << ",";
  _dbg(sdbg + 1, t...);
}
template <class t>
t mag(t a) {
  return a > 0 ? a : -a;
}
int tc = 1;
int x, y, h, w;
char type;
int escape() {
  int n;
  cin >> n;
  int mxx = 0, mxy = 0;
  for (__typeof(n) i = (0) - ((0) > (n)); i != (n) - ((0) > (n));
       i += 1 - 2 * ((0) > (n))) {
    cin >> type >> x >> y;
    if (x < y) swap(x, y);
    if (type == '+')
      mxx = max(mxx, x), mxy = max(mxy, y);
    else if (mxx <= x and mxy <= y)
      cout << "YES\n";
    else
      cout << "NO\n";
  }
  return 0;
}
int main() {
  cout.precision(std::numeric_limits<double>::max_digits10);
  ios_base::sync_with_stdio(false);
  while (tc--) {
    escape();
  }
}
