#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ;
  long long q, x, y, mx_x = 0, mx_y = 0;
  char s[5];
  scanf("%lld", &q);
  while (q--) {
    scanf("%s", s);
    scanf("%lld %lld", &x, &y);
    if (x < y) swap(x, y);
    if (s[0] == '+') {
      mx_x = max(mx_x, x);
      mx_y = max(mx_y, y);
    } else {
      if (mx_x <= x && mx_y <= y)
        printf("YES\n");
      else
        printf("NO\n");
    }
  }
}
