#include <bits/stdc++.h>
using namespace std;
int N;
int maxx, maxy;
int x, y;
int main() {
  cin >> N;
  for (int i = 0; i < N; ++i) {
    int x, y;
    string ch;
    cin >> ch;
    scanf("%d %d", &x, &y);
    if (x > y) swap(x, y);
    if (ch == "+") {
      maxx = max(maxx, x);
      maxy = max(maxy, y);
    } else {
      if (x >= maxx && y >= maxy) {
        printf("YES\n");
      } else
        printf("NO\n");
    }
  }
  return 0;
}
