self.seen_urls.add(url)
2. Tap the three dots at the top right corner and select Extension.
，这一点在快连下载-Letsvpn下载中也有详细论述
let goal = pixel，更多细节参见Safew下载
Cluster & Border Point Definition: The map is divided into clusters, and border points are identified using the Ford-Fulkerson based method.，推荐阅读safew官方下载获取更多信息