#include <bits/stdc++.h>
inline int read() {
  int x = 0, f = 1;
  char ch = getchar();
  while (!isdigit(ch)) {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (isdigit(ch)) {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
int n;
int max_x, max_y;
int main() {
  n = read();
  while (n--) {
    char opt = getchar();
    int x = read(), y = read();
    if (x > y) std::swap(x, y);
    if (opt == '+') {
      max_x = std::max(max_x, x);
      max_y = std::max(max_y, y);
    }
    if (opt == '?') {
      if (x >= max_x && y >= max_y) {
        printf("YES\n");
      } else {
        printf("NO\n");
      }
    }
  }
  return 0;
}
