#include <bits/stdc++.h>
const int MOD = 1e9;
const int N = 100003;
using namespace std;
vector<int> ans;
int main() {
  int n;
  cin >> n;
  int p, q;
  p = q = 0;
  for (int i = 0; i < n; i++) {
    char c;
    int x, y;
    cin >> c;
    scanf("%d", &x);
    scanf("%d", &y);
    if (x > y) swap(x, y);
    if (c == '+')
      p = max(p, x), q = max(q, y);
    else if (p <= x && q <= y)
      cout << "YES";
    else
      cout << "NO";
    cout << endl;
  }
  return 0;
}
