The 2-Vertex-Connected Spanning Subgraph problem (2VCSS) is among the most basic NP-hard (Survivable) Network Design problems: we are given an (unweighted) undirected graph $G$. Our goal is to find a subgraph $S$ of $G$ with the minimum number of edges which is $2$-vertex-connected, namely $S$ remains connected after the deletion of an arbitrary node. 2VCSS is well-studied in terms of approximation algorithms, and the current best (polynomial-time) approximation factor is $10/7$ by Heeger and Vygen [SIDMA'17] (improving on earlier results by Khuller and Vishkin [STOC'92] and Garg, Vempala and Singla [SODA'93]).

翻译：$2$-顶点连通生成子图问题（2VCSS）是最基本的NP难（可生存性）网络设计问题之一：给定一个（无权重）无向图$G$，目标是找到一个边数最少的子图$S$，使得$S$是$2$-顶点连通的，即删除任意一个节点后$S$仍保持连通。2VCSS在近似算法领域已有深入研究，当前最佳（多项式时间）近似因子为$10/7$，由Heeger和Vygen [SIDMA'17] 提出（改进了Khuller和Vishkin [STOC'92] 以及Garg、Vempala和Singla [SODA'93] 的早期结果）。