#include <bits/stdc++.h>
using namespace std;
int q, x, y, l = -1, r = -1, h, w;
char ch;
int main() {
  scanf("%d", &q);
  while (q--) {
    scanf(" %c", &ch);
    getchar();
    if (ch == '+') {
      scanf("%d %d", &x, &y);
      if (x > y) {
        swap(x, y);
      }
      l = max(x, l);
      r = max(y, r);
    }
    if (ch == '?') {
      scanf("%d %d", &h, &w);
      if ((h >= l && w >= r) || (h >= r && w >= l)) {
        printf("YES\n");
      } else {
        printf("NO\n");
      }
    }
  }
  return 0;
}
