#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long n;
  cin >> n;
  pair<long long, long long> p1;
  pair<long long, long long> p2;
  long long mx = -1, my = -1;
  long long a, b;
  while (n--) {
    char c;
    long long x, y;
    cin >> c >> x >> y;
    if (c == '+') {
      if (x < y) swap(x, y);
      mx = max(mx, x);
      my = max(my, y);
    } else {
      if (x < y) swap(x, y);
      if (mx <= x and my <= y)
        printf("YES\n");
      else
        printf("NO\n");
    }
  }
  return 0;
}
