#include <bits/stdc++.h>
using namespace std;
int m1 = 0, m2 = 0;
int n;
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    char c;
    cin >> c;
    int a, b;
    scanf("%d", &a);
    scanf("%d", &b);
    if (c == '+') {
      m1 = max(m1, max(a, b));
      m2 = max(m2, min(a, b));
    }
    if (c == '?') {
      if (m1 <= max(a, b) && m2 <= min(a, b)) {
        printf("YES\n");
      } else {
        printf("NO\n");
      }
    }
  }
  return 0;
}
