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: "contextual equivalence for higher order pi calculus revisited"
  Abstract: The higher-order pi-calculus is an extension of the pi-calculus to allow#N#communication of abstractions of processes rather than names alone. It has been#N#studied intensively by Sangiorgi in his thesis where a characterisation of a#N#contextual equivalence for higher-order pi-calculus is provided using labelled#N#transition systems and normal bisimulations. Unfortunately the proof technique#N#used there requires a restriction of the language to only allow finite types.#N#We revisit this calculus and offer an alternative presentation of the labelled#N#transition system and a novel proof technique which allows us to provide a#N#fully abstract characterisation of contextual equivalence using labelled#N#transitions and bisimulations for higher-order pi-calculus with recursive types#N#also.

Connected through hyperedge HE-1 (induced by source paper "core higher order session processes tractable equivalences and relative expressiveness"):
  with members:
    - "musings on encodings and expressiveness"
    - "typing copyless message passing"
    - "comparing the expressive power of the synchronous and asynchronous pi calculi"

Connected through hyperedge HE-2 (induced by source paper "modelling mac layer communications in wireless systems"):
  with members:
    - "modelling probabilistic wireless networks"
    - "a timed calculus for mobile ad hoc networks"

Connected through hyperedge HE-3 (induced by source paper "open bisimulation for quantum processes"):
  with members:
    - "logical metric and algorithmic characterisations of probabilistic bisimulation"

Connected through hyperedge HE-4 (induced by source paper "a verified algebra for linked data"):
  with members:
    - "semantics and complexity of sparql"

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)