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: "systematic abstraction of abstract machines"
  Abstract: We describe a derivational approach to abstract interpretation that yields novel and transparently sound static analyses when applied to well-established abstract machines for higher-order and imperative programming languages. To demonstrate the technique and support our claim, we transform the CEK machine of Felleisen and Friedman, a lazy variant of Krivine's machine, and the stack-inspecting CM machine of Clements and Felleisen into abstract interpretations of themselves. The resulting analyses bound temporal ordering of program events; predict return-flow and stack-inspection behavior; and approximate the flow and evaluation of by-need parameters. For all of these machines, we find that a series of well-known concrete machine refactorings, plus a technique of store-allocated continuations, leads to machines that abstract into static analyses simply by bounding their stores. We demonstrate that the technique scales up uniformly to allow static analysis of realistic language features, including tail calls, conditionals, side effects, exceptions, first-class continuations, and even garbage collection. In order to close the gap between formalism and implementation, we provide translations of the mathematics as running Haskell code for the initial development of our method.

Connected through hyperedge HE-1 (induced by source paper "abstracting definitional interpreters functional pearl"):
  with members:
    - "pushdown control flow analysis for free"
    - "galois transformers and modular abstract interpreters reusable metatheory for program analysis"
    - "soft contract verification"
    - "pushdown flow analysis with abstract garbage collection"
    - "simulation of two way pushdown automata revisited"
    - "abstracting abstract control extended"
    - "introspective pushdown analysis of higher order programs"
    - "cfa2 a context free approach to control flow analysis"

Connected through hyperedge HE-2 (induced by source paper "higher order symbolic execution for contract verification and refutation"):
  with members:
    - "type targeted testing"
    - "higher order symbolic execution via contracts"

Connected through hyperedge HE-3 (induced by source paper "soft contract verification"):
  with members:
    - "abstracting abstract control extended"
    - "concrete semantics for pushdown analysis the essence of summarization"
    - "dependent types for javascript"
    - "higher order symbolic execution via contracts"
    - "abstracting abstract machines"

Connected through hyperedge HE-4 (induced by source paper "pushdown flow analysis with abstract garbage collection"):
  with members:
    - "deciding k cfa is complete for exptime"
    - "concrete semantics for pushdown analysis the essence of summarization"
    - "introspective pushdown analysis of higher order programs"
    - "cfa2 a context free approach to control flow analysis"
    - "pushdown control flow analysis of higher order programs"

Connected through hyperedge HE-5 (induced by source paper "abstracting abstract control extended"):
  with members:
    - "simulation of two way pushdown automata revisited"
    - "optimizing abstract abstract machines"
    - "introspective pushdown analysis of higher order programs"
    - "cfa2 a context free approach to control flow analysis"
    - "pushdown control flow analysis of higher order programs"
    - "abstracting abstract machines"
    - "first order and temporal logics for nested words"

Connected through hyperedge HE-6 (induced by source paper "optimizing abstract abstract machines"):
  with members:
    - "automatic verification of erlang style concurrency"
    - "introspective pushdown analysis of higher order programs"
    - "abstracting abstract machines a systematic approach to higher order program analysis"
    - "cfa2 a context free approach to control flow analysis"
    - "higher order symbolic execution via contracts"

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)