#include <bits/stdc++.h>
#pragma optimization_level 3
#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math,O3")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
using namespace std;
const long long N = 1e6 + 5;
const long long mod = 998244353;
const long long INF = 0x7f7f7f7f7f7f7f7f;
const int INFi = 0x7f7f7f7f;
long long test = 1, q;
void solve() {
  int max1 = 0, max2 = 0;
  cin >> q;
  while (q--) {
    char x;
    int l, r;
    cin >> x >> l >> r;
    if (x == '+') {
      if (l < r) swap(l, r);
      max1 = max(max1, l);
      max2 = max(max2, r);
    } else {
      if (l < r) swap(l, r);
      if (l >= max1 and r >= max2)
        cout << "YES"
             << "\n";
      else
        cout << "NO"
             << "\n";
    }
  }
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cout << fixed;
  cout << setprecision(15);
  ;
  for (int i = 1; i <= test; i++) {
    solve();
  }
}
