#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("Ofast,no-stack-protector")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC optimize("unroll-loops")
long long A[1000005];
long long B[1000005];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  long long tst = 1;
  for (long long tt = 1; tt <= tst; tt++) {
    long long n, mn = 0, mx = 0;
    cin >> n;
    while (n--) {
      char ch;
      long long x, y;
      cin >> ch >> x >> y;
      if (x > y) swap(x, y);
      if (ch == '+') {
        mn = max(mn, x);
        mx = max(mx, y);
      } else {
        if (x >= mn && y >= mx)
          cout << "YES" << endl;
        else
          cout << "NO" << endl;
      }
    }
  }
  return 0;
}
