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: "pancake flipping is hard"
  Abstract: Pancake Flipping is the problem of sorting a stack of pancakes of different sizes (that is, a permutation), when the only allowed operation is to insert a spatula anywhere in the stack and to flip the pancakes above it (that is, to perform a prefix reversal). In the burnt variant, one side of each pancake is marked as burnt, and it is required to finish with all pancakes having the burnt side down. Computing the optimal scenario for any stack of pancakes and determining the worst-case stack for any stack size have been challenges over more than three decades. Beyond being an intriguing combinatorial problem in itself, it also yields applications, e.g. in parallel computing and computational biology.#R##N##R##N#In this paper, we show that the Pancake Flipping problem, in its original (unburnt) variant, is NP-hard, thus answering the long-standing question of its computational complexity.

Connected through hyperedge HE-1 (induced by source paper "shortest reconfiguration of perfect matchings via alternating cycles"):
  with members:
    - "the perfect matching reconfiguration problem"
    - "shortest reconfiguration of matchings"
    - "the time complexity of permutation routing via matching token swapping and a variant"
    - "flip distance between triangulations of a simple polygon is np complete"
    - "shortest reconfiguration of sliding tokens on a caterpillar"
    - "flip distance between triangulations of a planar point set is apx hard"
    - "finding shortest paths between graph colourings"
    - "shortest reconfiguration paths in the solution space of boolean formulas"

Connected through hyperedge HE-2 (induced by source paper "token swapping on trees"):
  with members:
    - "swapping colored tokens on graphs"
    - "the time complexity of permutation routing via matching token swapping and a variant"
    - "the time complexity of the token swapping problem and its parallel variants"
    - "approximation and hardness for token swapping"
    - "pebble games proof complexity and time space trade offs"
    - "the complexity of change"
    - "an efficient algorithm for the diameter of cayley graphs generated by transposition trees"
    - "playing games with algorithms algorithmic combinatorial game theory"

Connected through hyperedge HE-3 (induced by source paper "on the number of pancake stacks requiring four flips to be sorted"):
  with members:
    - "cycles in the burnt pancake graphs"
    - "on average and highest number of flips in pancake sorting"

Connected through hyperedge HE-4 (induced by source paper "cycles in the burnt pancake graphs"):
  with members:
    - "on average and highest number of flips in pancake sorting"

Connected through hyperedge HE-5 (induced by source paper "rearrangement problems with duplicated genomic markers"):
  with members:
    - "on sampling scj rearrangement scenarios"
    - "sorting by transpositions is difficult"
    - "polynomial time sortable stacks of burnt pancakes"
    - "genome halving by block interchange"
    - "on the complexity of rearrangement problems under the breakpoint distance"
    - "the zero exemplar distance problem"

Connected through hyperedge HE-6 (induced by source paper "the distribution of cycles in breakpoint graphs of signed permutations"):
  with members:
    - "sorting by transpositions is difficult"
    - "polynomial time sortable stacks of burnt pancakes"

Connected through hyperedge HE-7 (induced by source paper "lower bounding edit distances between permutations"):
  with members:
    - "sorting by transpositions is difficult"

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)