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 design of gp 2"
  Abstract: This papers deﬁnes the syntax and semantics of GP 2, a revised version of the graph programminglanguageGP. New concepts are illustrated and explainedwith exampleprograms. Changesto the ﬁrstversion of GP include an improved type system for labels, a built-in marking mechanism for nodesand edges, a more powerful edgepredicate for conditional rule schemata, and functions returningthe indegree and outdegree of matched nodes. Moreover, the semantics of the branching and loopstatement have been simpliﬁed to allow their efﬁcient imple mentation.

Connected through hyperedge HE-1 (induced by source paper "improving the gp 2 compiler"):
  with members:
    - "efficient graph rewriting"
    - "verifying monadic second order properties of graph programs"

Connected through hyperedge HE-2 (induced by source paper "efficient graph rewriting"):
  with members:
    - "verifying monadic second order properties of graph programs"

Connected through hyperedge HE-3 (induced by source paper "a semantics comparison workbench for a concurrent asynchronous distributed programming language"):
  with members:
    - "an interference free programming model for network objects"
    - "a graph based semantics workbench for concurrent asynchronous programs"
    - "on the verification of scoop programs"
    - "towards practical graph based verification for an object oriented concurrency model"
    - "verifying monadic second order properties of graph programs"
    - "efficient and reasonable object oriented concurrency"

Connected through hyperedge HE-4 (induced by source paper "a unification algorithm for gp 2 long version"):
  with members:
    - "a reference interpreter for the graph programming language gp 2"

Connected through hyperedge HE-5 (induced by source paper "reasoning about graph programs"):
  with members:
    - "a reference interpreter for the graph programming language gp 2"
    - "graphs as models preface"
    - "verifying monadic second order properties of graph programs"

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)