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 simple proof that the n 2 1 puzzle is hard"
  Abstract: Abstract   The 15 puzzle is a classic reconfiguration puzzle with fifteen uniquely labeled unit squares within a    4  ×  4    board in which the goal is to slide the squares (without ever overlapping) into a target configuration. By generalizing the puzzle to an    n  ×  n    board with      n    2    −  1    squares, we can study the computational complexity of problems related to the puzzle; in particular, we consider the problem of determining whether a given end configuration can be reached from a given start configuration via at most a given number of moves. This problem was shown NP-complete in  [1] . We provide an alternative simpler proof of this fact by reduction from the rectilinear Steiner tree problem.

Connected through hyperedge HE-1 (induced by source paper "shortest reconfiguration sequence for sliding tokens on spiders"):
  with members:
    - "token sliding on split graphs"
    - "token sliding on chordal graphs"
    - "parameterized complexity of graph constraint logic"
    - "shortest reconfiguration of sliding tokens on a caterpillar"
    - "reconfiguring independent sets in claw free graphs"
    - "reconfiguration over tree decompositions"
    - "linear time algorithm for sliding tokens on trees"
    - "on the parameterized complexity of reconfiguration problems"

Connected through hyperedge HE-2 (induced by source paper "star routing between vehicle routing and vertex cover"):
  with members:
    - "approximation algorithms for tsp with neighborhoods in the plane"

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.CC(Computational Complexity)