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: "characterizing the np pspace gap in the satisfiability problem for modal logic"
  Abstract: There has been a great of work on characterizing the complexity of the satisfiability and validity problem for modal logics. In particular, Ladner showed that the validity problem for all logics between K, T, and S4 is {\sl PSPACE}-complete, while for S5 it is {\sl NP}-complete. We show that, in a precise sense, it is \emph{negative introspection}, the axiom $\neg K p \rimp K \neg K p$, that causes the gap. In a precise sense, if we require this axiom, then the satisfiability problem is {\sl NP}-complete; without it, it is {\sl PSPACE}-complete.

Connected through hyperedge HE-1 (induced by source paper "modal logics with hard diamond free fragments"):
  with members:
    - "does treewidth help in modal satisfiability"
    - "parameterized modal satisfiability"
    - "generalized modal satisfiability"
    - "deciding regular grammar logics with converse through first order logic"
    - "the complexity of poor man s logic"

Connected through hyperedge HE-2 (induced by source paper "does treewidth help in modal satisfiability"):
  with members:
    - "tree width for first order formulae"
    - "a note on the complexity of the satisfiability problem for graded modal logics"
    - "parameterized modal satisfiability"
    - "generalized modal satisfiability"
    - "on the complexity of elementary modal logics"

Connected through hyperedge HE-3 (induced by source paper "pspace bounds for rank 1 modal logics"):
  with members:
    - "pspace reasoning for graded modal logics"

Connected through hyperedge HE-4 (induced by source paper "on the complexity of elementary modal logics"):
  with members:
    - "pspace bounds for rank 1 modal logics"

Connected through hyperedge HE-5 (induced by source paper "reasoning about knowledge of unawareness"):
  with members:
    - "extensive games with possibly unaware players"
    - "interactive unawareness revisited"
    - "multi agent only knowing"

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.LO(Logic in Computer Science)