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: "stackelberg network pricing is hard to approximate"
  Abstract: In the Stackelberg network pricing problem, one has to assign tariffs to a certain subset of the arcs of a given transportation network. The aim is to maximize the amount paid by the user of the network, knowing that the user will take a shortest st-path once the tariffs are fixed. (Roch et al., Networks, 46 (2005), 57–67) proved that this problem is NP-hard, and gave an O(log m)-approximation algorithm, where m denote the number of arcs to be priced. In this note, we show that the problem is also APX-hard. © 2010 Wiley Periodicals, Inc. NETWORKS, Vol. 57(2), 117–120 2011 © 2011 Wiley Periodicals, Inc.

Connected through hyperedge HE-1 (induced by source paper "negative prices in network pricing games"):
  with members:
    - "toll caps in privatized road networks"
    - "inefficiencies in network models a graph theoretic perspective"
    - "approximate revenue maximization with multiple items"
    - "matroids are immune to braess paradox"
    - "new complexity results and algorithms for the minimum tollbooth problem"
    - "stackelberg shortest path tree game revisited"
    - "the stackelberg minimum spanning tree game"
    - "improved hardness of approximation for stackelberg shortest path pricing"

Connected through hyperedge HE-2 (induced by source paper "specializations and generalizations of the stackelberg minimum spanning tree game"):
  with members:
    - "the stackelberg minimum spanning tree game on planar and bounded treewidth graphs"
    - "the stackelberg minimum spanning tree game"
    - "improved hardness of approximation for stackelberg shortest path pricing"
    - "stackelberg network pricing games"

Connected through hyperedge HE-3 (induced by source paper "stackelberg shortest path tree game revisited"):
  with members:
    - "the stackelberg minimum spanning tree game"
    - "improved hardness of approximation for stackelberg shortest path pricing"
    - "stackelberg network pricing games"

Connected through hyperedge HE-4 (induced by source paper "stackelberg pricing is hard to approximate within 2 epsilon"):
  with members:
    - "the stackelberg minimum spanning tree game on planar and bounded treewidth graphs"
    - "the stackelberg minimum spanning tree game"
    - "improved hardness of approximation for stackelberg shortest path pricing"
    - "stackelberg network pricing games"

Connected through hyperedge HE-5 (induced by source paper "improved hardness of approximation for stackelberg shortest path pricing"):
  with members:
    - "the stackelberg minimum spanning tree game"
    - "stackelberg network pricing games"

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)