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: "on separation by locally testable and locally threshold testable languages"
  Abstract: A separator for two languages is a third language containing the first one#N#and disjoint from the second one. We investigate the following decision#N#problem: given two regular input languages, decide whether there exists a#N#locally testable (resp. a locally threshold testable) separator. In both cases,#N#we design a decision procedure based on the occurrence of special patterns in#N#automata accepting the input languages. We prove that the problem is#N#computationally harder than deciding membership. The correctness proof of the#N#algorithm yields a stronger result, namely a description of a possible#N#separator. Finally, we discuss the same problem for context-free input#N#languages.

Connected through hyperedge HE-1 (induced by source paper "partially ordered automata and piecewise testability"):
  with members:
    - "the covering problem"
    - "complexity of detectability opacity and a diagnosability for modular discrete event systems"
    - "complexity of universality and related problems for partially ordered nfas"
    - "separability by piecewise testable languages is ptime complete"
    - "complexity of deciding detectability in discrete event systems"
    - "piecewise testable languages and nondeterministic automata"
    - "the height of piecewise testable languages and the complexity of the logic of subwords"
    - "separating regular languages by piecewise testable and unambiguous languages"

Connected through hyperedge HE-2 (induced by source paper "separating regular languages with first order logic"):
  with members:
    - "separating regular languages by piecewise testable and unambiguous languages"
    - "efficient separability of regular languages by subsequences and suffixes"

Connected through hyperedge HE-3 (induced by source paper "going higher in the first order quantifier alternation hierarchy on words"):
  with members:
    - "separating regular languages with first order logic"
    - "separating regular languages by piecewise testable and unambiguous languages"
    - "efficient separability of regular languages by subsequences and suffixes"

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.FL(Formal Languages and Automata Theory)