#include <bits/stdc++.h>
using namespace std;
int main() {
  int T, N, M, X, Y, W;
  scanf("%d", &N);
  long long a, b, aa = 0, bb = 0;
  while (N--) {
    char S;
    getchar();
    scanf("%c", &S);
    getchar();
    scanf("%d %d", &X, &Y);
    a = min(X, Y);
    b = max(X, Y);
    if (S == '+') {
      aa = max(aa, a);
      bb = max(bb, b);
    } else if (S == '?') {
      if (aa <= a && bb <= b)
        printf("YES\n");
      else
        printf("NO\n");
    }
  }
  return 0;
}
