#include <bits/stdc++.h>
using namespace std;
int main() {
  int q;
  scanf("%d\n", &q);
  int mx = 0, my = 0;
  for (int t = 0; t < q; t++) {
    char c;
    int x, y;
    scanf("%c %d %d\n", &c, &x, &y);
    if (x > y) {
      swap(x, y);
    }
    if (c == '+') {
      mx = max(mx, x);
      my = max(my, y);
    } else {
      printf(mx <= x && my <= y ? "YES\n" : "NO\n");
    }
  }
  return 0;
}
