  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]).
