#include <bits/stdc++.h>
using namespace std;
void Swap(int &a, int &b) {
  a = a ^ b;
  b = a ^ b;
  a = a ^ b;
}
int Max(int a, int b) {
  if (a > b) return a;
  return b;
}
int Scan() {
  int res = 0;
  char ch;
  ch = getchar();
  if (ch >= '0' && ch <= '9') res = ch - '0';
  while ((ch = getchar()) >= '0' && ch <= '9') res = res * 10 + (ch - '0');
  return res;
}
int main() {
  int T = Scan();
  int X = 0, Y = 0;
  while (T--) {
    char c;
    cin >> c;
    int a = Scan();
    int b = Scan();
    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;
  }
}
