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: "functional units for natural numbers"
  Abstract: Interaction with services provided by an execution environ- ment forms part of the behaviours exhibited by instruction sequences under execution. Mechanisms related to the kind of interaction in ques- tion have been proposed in the setting of thread algebra. Like thread, service is an abstract behavioural concept. The concept of a functional unit is similar to the concept of a service, but more concrete. A state space is inherent in the concept of a functional unit, whereas it is not inherent in the concept of a service. In this paper, we establish the exis- tence of a universal computable functional unit for natural numbers and related results.

Connected through hyperedge HE-1 (induced by source paper "from functions to object orientation by abstraction"):
  with members:
    - "a process calculus with finitary comprehended terms"
    - "instruction sequence processing operators"
    - "on the expressiveness of single pass instruction sequences"
    - "indirect jumps improve instruction sequence performance"
    - "concurrent models for object execution"
    - "communicating concurrent functions"
    - "concurrent models for function execution"
    - "thread algebra for poly threading"

Connected through hyperedge HE-2 (induced by source paper "instruction sequence processing operators"):
  with members:
    - "on the expressiveness of single pass instruction sequences"
    - "indirect jumps improve instruction sequence performance"
    - "on the behaviours produced by instruction sequences under execution"
    - "on the operating unit size of load store architectures"
    - "a thread calculus with molecular dynamics"
    - "an instruction sequence semigroup with involutive anti automorphisms"
    - "autosolvability of halting problem instances for instruction sequences"
    - "program algebra with a jump shift instruction"

Connected through hyperedge HE-3 (induced by source paper "on the contribution of backward jumps to instruction sequence expressiveness"):
  with members:
    - "instruction sequence processing operators"
    - "autosolvability of halting problem instances for instruction sequences"
    - "instruction sequences and non uniform complexity theory"

Connected through hyperedge HE-4 (induced by source paper "autosolvability of halting problem instances for instruction sequences"):
  with members:
    - "instruction sequence processing operators"
    - "program algebra with a jump shift instruction"

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)