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