#include <bits/stdc++.h>
using namespace std;
int n, x, y, lx = -1, ly;
char t;
int main() {
  scanf("%d", &n);
  while (n--) {
    scanf(" %c %d %d", &t, &x, &y);
    if (x > y) swap(x, y);
    if (t == '+') {
      if (lx == -1) {
        lx = x;
        ly = y;
      } else {
        lx = max(lx, x);
        ly = max(ly, y);
      }
    } else if (t == '?') {
      puts((x >= lx && y >= ly) ? "YES" : "NO");
    } else
      assert(false);
  }
  return 0;
}
