human: Given a node-centered hypergraph: <hypergraph>, where nodes represent papers and hyperedges represent sets of papers co-cited by a source paper.

Details of the hypergraph:
Center node: "a 2k vertex kernel for maximum internal spanning tree"
  Abstract: We consider the parameterized version of the maximum internal spanning tree problem, which, given an $n$-vertex graph and a parameter $k$, asks for a spanning tree with at least $k$ internal vertices. Fomin et al. [J. Comput. System Sci., 79:1-6] crafted a very ingenious reduction rule, and showed that a simple application of this rule is sufficient to yield a $3k$-vertex kernel. Here we propose a novel way to use the same reduction rule, resulting in an improved $2k$-vertex kernel. Our algorithm applies first a greedy procedure consisting of a sequence of local exchange operations, which ends with a local-optimal spanning tree, and then uses this special tree to find a reducible structure. As a corollary of our kernel, we obtain a deterministic algorithm for the problem running in time $4^k \cdot n^{O(1)}$.

Connected through hyperedge HE-1 (induced by source paper "approximation algorithms for the maximum weight internal spanning tree problem"):
  with members:
    - "an approximation algorithm for maximum internal spanning tree"
    - "algorithm for finding k vertex out trees and its application to k internal out branching problem"
    - "a linear vertex kernel for maximum internal spanning tree"

Connected through hyperedge HE-2 (induced by source paper "an approximation algorithm for maximum internal spanning tree"):
  with members:
    - "a 4 3 approximation algorithm for finding a spanning tree to maximize its internal vertices"
    - "algorithm for finding k vertex out trees and its application to k internal out branching problem"
    - "a linear vertex kernel for maximum internal spanning tree"

Connected through hyperedge HE-3 (induced by source paper "spotting trees with few leaves"):
  with members:
    - "representative sets of product families"
    - "representative families a unified tradeoff based approach"
    - "mixing color coding related techniques"
    - "solving connectivity problems parameterized by treewidth in single exponential time"
    - "narrow sieves for parameterized paths and packings"
    - "determinant sums for undirected hamiltonicity"
    - "algorithm for finding k vertex out trees and its application to k internal out branching problem"
    - "a linear vertex kernel for maximum internal spanning tree"

Connected through hyperedge HE-4 (induced by source paper "mixing color coding related techniques"):
  with members:
    - "representative sets of product families"
    - "representative families a unified tradeoff based approach"
    - "deterministic parameterized algorithms for matching and packing problems"
    - "narrow sieves for parameterized paths and packings"
    - "determinant sums for undirected hamiltonicity"
    - "algorithm for finding k vertex out trees and its application to k internal out branching problem"
    - "a linear vertex kernel for maximum internal spanning tree"
    - "minimum leaf out branching and related problems"

Question: Please tell me which class the center node belongs to. The 40 classes are: cs.NA(Numerical Analysis), cs.MM(Multimedia), cs.LO(Logic in Computer Science), cs.CY(Computers and Society), cs.CR(Cryptography and Security), cs.DC(Distributed, Parallel, and Cluster Computing), cs.HC(Human-Computer Interaction), cs.CE(Computational Engineering, Finance, and Science), cs.NI(Networking and Internet Architecture), cs.CC(Computational Complexity), cs.AI(Artificial Intelligence), cs.MA(Multiagent Systems), cs.GL(General Literature), cs.NE(Neural and Evolutionary Computing), cs.SC(Symbolic Computation), cs.AR(Hardware Architecture), cs.CV(Computer Vision and Pattern Recognition), cs.GR(Graphics), cs.ET(Emerging Technologies), cs.SY(Systems and Control), cs.CG(Computational Geometry), cs.OH(Other Computer Science), cs.PL(Programming Languages), cs.SE(Software Engineering), cs.LG(Machine Learning), cs.SD(Sound), cs.SI(Social and Information Networks), cs.RO(Robotics), cs.IT(Information Theory), cs.PF(Performance), cs.CL(Computation and Language), cs.IR(Information Retrieval), cs.MS(Mathematical Software), cs.FL(Formal Languages and Automata Theory), cs.DS(Data Structures and Algorithms), cs.OS(Operating Systems), cs.GT(Computer Science and Game Theory), cs.DB(Databases), cs.DL(Digital Libraries), cs.DM(Discrete Mathematics). Directly output the class name.

gpt: cs.DS(Data Structures and Algorithms)