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: "elaborating intersection and union types"
  Abstract: Designing and implementing typed programming languages is hard. Every new type system feature requires extending the metatheory and implementation, which are often complicated and fragile. To ease this process, we would like to provide general mechanisms that subsume many different features. #R##N#In modern type systems, parametric polymorphism is fundamental, but intersection polymorphism has gained little traction in programming languages. Most practical intersection type systems have supported only refinement intersections, which increase the expressiveness of types (more precise properties can be checked) without altering the expressiveness of terms; refinement intersections can simply be erased during compilation. In contrast, unrestricted intersections increase the expressiveness of terms, and can be used to encode diverse language features, promising an economy of both theory and implementation. #R##N#We describe a foundation for compiling unrestricted intersection and union types: an elaboration type system that generates ordinary lambda-calculus terms. The key feature is a Forsythe-like merge construct. With this construct, not all reductions of the source program preserve types; however, we prove that ordinary call-by-value evaluation of the elaborated program corresponds to a type-preserving evaluation of the source program. #R##N#We also describe a prototype implementation and applications of unrestricted intersections and unions: records, operator overloading, and simulating dynamic typing.

Connected through hyperedge HE-1 (induced by source paper "bidirectional typing"):
  with members:
    - "the exp log normal form of types decomposing extensional equality and representing terms compactly"
    - "sums of uncertainty refinements go gradual"
    - "deciding equivalence with sums and the empty type"

Connected through hyperedge HE-2 (induced by source paper "the delta calculus syntax and types"):
  with members:
    - "the delta framework"
    - "the algebraic intersection type unification problem"

Connected through hyperedge HE-3 (induced by source paper "isomorphism of intersection and union types"):
  with members:
    - "simply typed lambda calculus modulo type isomorphisms"
    - "on isomorphism of functional intersection and union types"

Connected through hyperedge HE-4 (induced by source paper "isomorphisms considered as equalities projecting functions and enhancing partial application through an implementation of λ"):
  with members:
    - "the vectorial λ calculus"
    - "quantum superpositions and projective measurement in the lambda calculus"
    - "simply typed lambda calculus modulo type isomorphisms"
    - "call by value non determinism in a linear logic type discipline"
    - "non idempotent intersection types and strong normalisation"
    - "bounding normalization time through intersection types"
    - "a system f accounting for scalars"

Connected through hyperedge HE-5 (induced by source paper "trust but verify two phase typing for dynamic languages"):
  with members:
    - "soft contract verification"
    - "untangling typechecking of intersections and unions"

Connected through hyperedge HE-6 (induced by source paper "elaborating evaluation order polymorphism"):
  with members:
    - "complete and easy bidirectional typechecking for higher rank polymorphism"

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)