#include <bits/stdc++.h>
int main() {
  int n;
  scanf("%d", &n);
  int maxx = 0, maxy = 0;
  static char type;
  for (int i = 0; i < n; i++) {
    int x = 0, y = 0;
    scanf(" %c%d%d", &type, &x, &y);
    if (x < y) {
      int tmp = x;
      x = y;
      y = tmp;
    }
    if (type == '+') {
      if (x > maxx) {
        maxx = x;
      }
      if (y > maxy) {
        maxy = y;
      }
    } else {
      if (x >= maxx && y >= maxy) {
        printf("YES\n");
      } else {
        printf("NO\n");
      }
    }
  }
}
