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 safe lambda calculus"
  Abstract: Safety is a syntactic condition of higher-order grammars that constrains#N#occurrences of variables in the production rules according to their#N#type-theoretic order. In this paper, we introduce the safe lambda calculus,#N#which is obtained by transposing (and generalizing) the safety condition to the#N#setting of the simply-typed lambda calculus. In contrast to the original#N#definition of safety, our calculus does not constrain types (to be#N#homogeneous). We show that in the safe lambda calculus, there is no need to#N#rename bound variables when performing substitution, as variable capture is#N#guaranteed not to happen. We also propose an adequate notion of beta-reduction#N#that preserves safety. In the same vein as Schwichtenberg's 1976#N#characterization of the simply-typed lambda calculus, we show that the numeric#N#functions representable in the safe lambda calculus are exactly the#N#multivariate polynomials; thus conditional is not definable. We also give a#N#characterization of representable word functions. We then study the complexity#N#of deciding beta-eta equality of two safe simply-typed terms and show that this#N#problem is PSPACE-hard. Finally we give a game-semantic analysis of safety: We#N#show that safe terms are denoted by `P-incrementally justified strategies'.#N#Consequently pointers in the game semantics of safe lambda-terms are only#N#necessary from order 4 onwards.

Connected through hyperedge HE-1 (induced by source paper "reducing lambda terms with traversals"):
  with members:
    - "normalisation by traversals"

Connected through hyperedge HE-2 (induced by source paper "on word and frontier languages of unsafe higher order grammars"):
  with members:
    - "typing weak msol properties"
    - "unboundedness and downward closures of higher order pushdown automata"

Connected through hyperedge HE-3 (induced by source paper "ordered tree pushdown systems"):
  with members:
    - "saturation algorithms for model checking pushdown systems"
    - "saturation of concurrent collapsible pushdown systems"
    - "model checking of ordered multi pushdown automata"
    - "strictness of the collapsible pushdown hierarchy"
    - "a finite semantics of simply typed lambda terms for infinite runs of automata"

Connected through hyperedge HE-4 (induced by source paper "complexity of model checking recursion schemes for fragments of the modal mu calculus"):
  with members:
    - "the complexity of games on higher order pushdown automata"
    - "a finite semantics of simply typed lambda terms for infinite runs of 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.PL(Programming Languages)