#include <bits/stdc++.h>
using namespace std;
const double pi = 2 * acos(0.0);
const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, -1, 0, 1};
const int dx8[] = {-1, 0, 1, 0, 1, 1, -1, -1};
const int dy8[] = {0, -1, 0, 1, 1, -1, 1, -1};
void solve() {
  long long n;
  cin >> n;
  long long x1 = -1, y1 = -1;
  long long x2 = -1, y2 = -1;
  while (n--) {
    char ch;
    cin >> ch;
    if (ch == '+') {
      long long a, b;
      cin >> a >> b;
      if (a > b) swap(a, b);
      x1 = max(a, x1);
      y1 = max(b, y1);
      x2 = max(b, x2);
      y2 = max(a, y2);
    } else {
      long long a, b;
      cin >> a >> b;
      if ((a >= x1 and b >= y1) || (a >= x2 and b >= y2))
        cout << "YES" << '\n';
      else
        cout << "NO" << '\n';
    }
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  solve();
}
