#include <bits/stdc++.h>
using namespace std;
int main() {
  int T;
  scanf("%d", &T);
  int X = 0, Y = 0;
  while (T--) {
    int a, b;
    char c;
    cin >> c;
    scanf("%d%d", &a, &b);
    if (a < b) swap(a, b);
    if (c == '+')
      X = max(X, a), Y = max(Y, b);
    else
      cout << ((a >= X && b >= Y) ? "YES" : "NO") << endl;
  }
}
