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: "a theory of explicit substitutions with safe and full composition"
  Abstract: Many different systems with explicit substitutions have been proposed to#N#implement a large class of higher-order languages. Motivations and challenges#N#that guided the development of such calculi in functional frameworks are#N#surveyed in the first part of this paper. Then, very simple technology in named#N#variable-style notation is used to establish a theory of explicit substitutions#N#for the lambda-calculus which enjoys a whole set of useful properties such as#N#full composition, simulation of one-step beta-reduction, preservation of#N#beta-strong normalisation, strong normalisation of typed terms and confluence#N#on metaterms. Normalisation of related calculi is also discussed.

Connected through hyperedge HE-1 (induced by source paper "reduction monads and their signatures"):
  with members:
    - "modular specification of monads through higher order presentations"
    - "signatures and models for syntax and operational semantics in the presence of variable binding"
    - "high level signatures and initial semantics"
    - "lecture notes on the lambda calculus"
    - "modules over relative monads for syntax and semantics"
    - "monads need not be endofunctors"
    - "cartesian closed 2 categories and permutation equivalence in higher order rewriting"
    - "second order algebraic theories"

Connected through hyperedge HE-2 (induced by source paper "signatures and models for syntax and operational semantics in the presence of variable binding"):
  with members:
    - "high level signatures and initial semantics"
    - "lecture notes on the lambda calculus"
    - "monads need not be endofunctors"
    - "cartesian closed 2 categories and permutation equivalence in higher order rewriting"
    - "second order algebraic theories"
    - "initial semantics for strengthened signatures"
    - "closed nominal rewriting and efficiently computable nominal algebra equality"

Connected through hyperedge HE-3 (induced by source paper "strong bisimulation for control operators"):
  with members:
    - "non idempotent types for classical calculi in natural deduction style"
    - "proof nets and the linear substitution calculus"
    - "a fully abstract semantics of lambda mu in the pi calculus"

Connected through hyperedge HE-4 (induced by source paper "non idempotent types for classical calculi in natural deduction style"):
  with members:
    - "non idempotent intersection types and strong normalisation"
    - "sound and complete typing for lambda mu"
    - "execution time of lambda terms via denotational semantics and intersection types"

Connected through hyperedge HE-5 (induced by source paper "non idempotent intersection types and strong normalisation"):
  with members:
    - "a convenient differential category"
    - "execution time of lambda terms via denotational semantics and intersection types"
    - "a proof of strong normalisation using domain theory"
    - "soft lambda calculus a language for polynomial time computation"

Connected through hyperedge HE-6 (induced by source paper "swapping a natural bridge between named and indexed explicit substitution calculi"):
  with members:
    - "polynomial size analysis of first order shapely functions"

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)