#include <bits/stdc++.h>
using namespace std;
int main() {
  int T;
  scanf("%d", &T);
  int maxx1 = 0, maxx2 = 0;
  while (T--) {
    char t[2];
    int x, y;
    scanf("%s%d%d", t, &x, &y);
    int a = max(x, y);
    int b = min(x, y);
    if (t[0] == '+') {
      maxx1 = max(maxx1, b);
      maxx2 = max(maxx2, a);
    } else {
      if (maxx1 <= b && maxx2 <= a) {
        printf("YES\n");
      } else
        printf("NO\n");
    }
  }
  return 0;
}
