#include <bits/stdc++.h>
const int N = 500010;
using namespace std;
int Q, T = 0, x, y, mx = 0, my = 0;
char pd;
int main() {
  scanf("%d", &Q);
  for (int i = 1; i <= Q; i++) {
    scanf("\n");
    scanf("%c%d%d", &pd, &x, &y);
    if (x > y) swap(x, y);
    if (pd == '+')
      mx = max(mx, x), my = max(my, y);
    else {
      if (mx > x || my > y)
        printf("NO\n");
      else
        printf("YES\n");
    }
  }
  return 0;
}
