#include <bits/stdc++.h>
using namespace std;
template <typename item>
item abs(item i) {
  if (i < 0) i = -i;
  return i;
}
template <class type>
type POW(type b, type p) {
  type res = 1;
  while (p) {
    if (p & 1) res *= b;
    b *= b;
    b %= 1000000007LL;
    res %= 1000000007LL;
    p /= 2;
  }
  return res;
}
int tc = 0;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  string s;
  int x, y, h, w, hh = -1, ww = -1;
  int t;
  cin >> t;
  while (t--) {
    cin >> s;
    if (s == "+") {
      cin >> x >> y;
      if (x > y) swap(x, y);
      hh = max(hh, x);
      ww = max(ww, y);
    } else {
      cin >> h >> w;
      if (h > w) swap(h, w);
      if (hh <= h and ww <= w)
        cout << "YES\n";
      else
        cout << "NO\n";
    }
  }
  return 0;
}
