#include <bits/stdc++.h>
using namespace std;
int t, x, y, min_x, min_y;
char c;
int main() {
  scanf("%d\n", &t);
  while (t--) {
    scanf("%c %d %d\n", &c, &x, &y);
    if (c == '+') {
      if (max(x, y) > min_x) {
        min_x = max(x, y);
      }
      if (min(x, y) > min_y) {
        min_y = min(x, y);
      }
    } else {
      if (max(x, y) < min_x || min(x, y) < min_y) {
        cout << "NO";
      } else {
        cout << "YES";
      }
      cout << endl;
    }
  }
  return 0;
}
