#include <bits/stdc++.h>
using namespace std;
const long long MOD = 1e9 + 7;
int main() {
  int N;
  scanf("%d", &N);
  while (getchar() != '\n') continue;
  int B = -1, C = -1;
  for (int i = 0; i < N; i++) {
    char a;
    int b, c;
    scanf("%c%d%d", &a, &b, &c);
    while (getchar() != '\n') continue;
    if (a == '+') {
      B = max(min(b, c), B);
      C = max(max(b, c), C);
    } else {
      if (min(b, c) < B || max(b, c) < C)
        printf("NO\n");
      else
        printf("YES\n");
    }
  }
  return 0;
}
