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: "the diagonal problem for higher order recursion schemes is decidable"
  Abstract: A non-deterministic recursion scheme recognizes a language of finite trees. This very expressive model can simulate, among others, higher-order pushdown automata with collapse. We show decidability of the diagonal problem for schemes. This result has several interesting consequences. In particular, it gives an algorithm that computes the downward closure of languages of words recognized by schemes. In turn, this has immediate application to separability problems and reachability analysis of concurrent systems.

Connected through hyperedge HE-1 (induced by source paper "intersection types for unboundedness problems"):
  with members:
    - "intersection types and counting"
    - "pumping lemma for higher order languages"
    - "on word and frontier languages of unsafe higher order grammars"
    - "relational semantics of linear logic and higher order model checking"
    - "ordered tree pushdown systems"
    - "finitary semantics of linear logic and higher order model checking"
    - "an approach to computing downward closures"
    - "regular cost functions part i logic and algebra over words"

Connected through hyperedge HE-2 (induced by source paper "recursion schemes the mso logic and the u quantifier"):
  with members:
    - "unboundedness and downward closures of higher order pushdown automata"
    - "ordered tree pushdown systems"
    - "an approach to computing downward closures"
    - "using models to model check recursive schemes"
    - "weak mso u with path quantifiers over infinite trees"
    - "io vs oi in higher order recursion schemes"
    - "weak mso with the unbounding quantifier"

Connected through hyperedge HE-3 (induced by source paper "ptl separability and closures for wqos on words"):
  with members:
    - "unboundedness and downward closures of higher order pushdown automata"
    - "demystifying reachability in vector addition systems"
    - "a characterization for decidable separability by piecewise testable languages"
    - "computing downward closures for stacked counter automata"

Connected through hyperedge HE-4 (induced by source paper "intersection types and counting"):
  with members:
    - "unboundedness and downward closures of higher order pushdown automata"
    - "ordered tree pushdown systems"
    - "strictness of the collapsible pushdown hierarchy"

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)