#include <bits/stdc++.h>
using namespace std;
const int MOD = 1e9 + 7;
const int n_ = 1e5 + 1000;
const long double PI = acos(-1.0);
long long gcd(long long a, long long b) { return (a ? gcd(b % a, a) : b); }
long long power(long long a, long long n) {
  long long p = 1;
  while (n > 0) {
    if (n % 2) {
      p = p * a;
    }
    n >>= 1;
    a *= a;
  }
  return p;
}
long long power(long long a, long long n, long long mod) {
  long long p = 1;
  while (n > 0) {
    if (n % 2) {
      p = p * a;
      p %= mod;
    }
    n >>= 1;
    a *= a;
    a %= mod;
  }
  return p % mod;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long n;
  cin >> n;
  long long max_x = INT_MIN;
  long long max_y = INT_MIN;
  for (int i = 0; i < n; i++) {
    char ch;
    long long num1, num2;
    cin >> ch >> num1 >> num2;
    if (ch == '+') {
      if (num1 < num2) {
        long long temp = num1;
        num1 = num2;
        num2 = temp;
      }
      if (max_x < num1) max_x = num1;
      if (max_y < num2) max_y = num2;
    } else if (ch == '?') {
      long long h = num1, w = num2;
      if ((max_x <= h && max_y <= w) || (max_x <= w && max_y <= h))
        cout << "YES\n";
      else
        cout << "NO\n";
    }
  }
}
