#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long int q;
  cin >> q;
  long long int a, b;
  a = b = -1ll;
  char c;
  long long int x, y;
  while (q--) {
    cin >> c;
    cin >> x >> y;
    if (x < y) {
      long long int temp = x;
      x = y;
      y = temp;
    }
    if (a == -1 && b == -1) {
      a = x;
      b = y;
      continue;
    }
    if (c == '+') {
      a = max(a, x);
      b = max(b, y);
    } else if (c == '?') {
      if ((x >= a && y >= b) || (x >= b && y >= a))
        cout << "YES" << endl;
      else
        cout << "NO" << endl;
    }
  }
  return 0;
}
