I. Introduction
In graph mining, various measures have been studied to extract dense subgraphs for extracting knowledge from various data represented as graphs. Among them, -core has been actively studied due to its simple definition and tractability, which aims at finding the maximal induced subgraph where each vertex has at least neighbors. The notion of -core helps identify a group of vertices which have high cohesiveness. The extraction of -cores has a wide spectrum of applications, such as social network visualization [1], anomalies detection [2], identifying influential spreaders [3], and predict development of biological systems [4].