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: "timed pushdown automata revisited"
  Abstract: This paper contains two results on timed extensions of pushdown automata (PDA). As our first result we prove that the model of dense-timed PDA of Abdulla et al. collapses: it is expressively equivalent to dense-timed PDA with timeless stack. Motivated by this result, we advocate the framework of first-order definable PDA, a specialization of PDA in sets with atoms, as the right setting to define and investigate timed extensions of PDA. The general model obtained in this way is Turing complete. As our second result we prove NEXPTIME upper complexity bound for the non-emptiness problem for an expressive subclass. As a byproduct, we obtain a tight EXPTIME complexity bound for a more restrictive subclass of PDA with timeless stack, thus subsuming the complexity bound known for dense-timed PDA.

Connected through hyperedge HE-1 (induced by source paper "timed systems through the lens of logic"):
  with members:
    - "non sequential theory of distributed systems"
    - "decidability of timed communicating automata"
    - "binary reachability of timed pushdown automata via quantifier elimination and cyclic order atoms"
    - "towards an efficient tree automata based technique for timed systems"
    - "analyzing timed systems using tree automata"
    - "monadic second order definable graph orderings"
    - "quantified ctl expressiveness and complexity"

Connected through hyperedge HE-2 (induced by source paper "timed context free temporal logics"):
  with members:
    - "event clock nested automata"
    - "on the decidability and complexity of metric temporal logic over finite words"

Connected through hyperedge HE-3 (induced by source paper "timed context free temporal logics extended version"):
  with members:
    - "event clock nested automata"

Connected through hyperedge HE-4 (induced by source paper "binary reachability of timed pushdown automata via quantifier elimination and cyclic order atoms"):
  with members:
    - "decidability of timed communicating automata"

Connected through hyperedge HE-5 (induced by source paper "synchronizing data words for register automata"):
  with members:
    - "complexity hierarchies beyond elementary"
    - "alternating register automata on finite words and trees"
    - "ackermannian and primitive recursive bounds with dickson s lemma"
    - "ltl with the freeze quantifier and register automata"
    - "on the freeze quantifier in constraint ltl decidability and complexity"

Connected through hyperedge HE-6 (induced by source paper "analyzing timed systems using tree automata"):
  with members:
    - "reachability problem for weak multi pushdown automata"
    - "model checking of ordered multi pushdown automata"

Connected through hyperedge HE-7 (induced by source paper "reachability analysis of first order definable pushdown systems"):
  with members:
    - "automata theory in nominal sets"
    - "saturation algorithms for model checking pushdown systems"
    - "reachability problem for weak multi pushdown automata"
    - "model checking of ordered multi pushdown automata"
    - "ltl with the freeze quantifier and register automata"
    - "alternating timed automata"

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.FL(Formal Languages and Automata Theory)