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 the index of simon s congruence for piecewise testability"
  Abstract: Simon's congruence, denoted by ~ n , relates words having the same subwords of length up to n. We show that, over a k-letter alphabet, the number of words modulo ~ n is in 2 ? ( n k - 1 log ? n ) . We provide upper and lower bounds for Simon's index for piecewise testability.This index depends on the length of considered subwords and the alphabet size.The previously known bounds focused on fixed length of subwords.Our bounds are relevant when alphabet size is fixed and length of subwords vary.They give a growth rate that is exponential and not doubly exponential.

Connected through hyperedge HE-1 (induced by source paper "scattered factor universality of words"):
  with members:
    - "k spectra of weakly c balanced words"
    - "languages ordered by the subword order"
    - "computing the k binomial complexity of the thue morse word"
    - "testing simon s congruence"
    - "multivariate fine grained complexity of longest common subsequence"
    - "decidability complexity and expressiveness of first order logic over the subword ordering"
    - "complexity of universality and related problems for partially ordered nfas"
    - "the complexity of downward closure comparisons"

Connected through hyperedge HE-2 (induced by source paper "computing the k binomial complexity of the thue morse word"):
  with members:
    - "automatic theorem proving in walnut"
    - "relations on words"
    - "testing k binomial equivalence"
    - "avoiding 2 binomial squares and cubes"

Connected through hyperedge HE-3 (induced by source paper "testing simon s congruence"):
  with members:
    - "alternating towers and piecewise testable separators"
    - "structure theorem and strict alternation hierarchy for fo2 on words"

Connected through hyperedge HE-4 (induced by source paper "on the height of towers of subsequences and prefixes"):
  with members:
    - "separability by piecewise testable languages is ptime complete"
    - "on upper and lower bounds on the length of alternating towers"
    - "a characterization for decidable separability by piecewise testable languages"
    - "alternating towers and piecewise testable separators"
    - "separating regular languages by piecewise testable and unambiguous languages"
    - "efficient separability of regular languages by subsequences and suffixes"

Connected through hyperedge HE-5 (induced by source paper "going higher in first order quantifier alternation hierarchies on words"):
  with members:
    - "separating regular languages with two quantifier alternations"
    - "separating regular languages with first order logic"
    - "going higher in the first order quantifier alternation hierarchy on words"
    - "separating regular languages by piecewise testable and unambiguous languages"
    - "efficient separability of regular languages by subsequences and suffixes"

Connected through hyperedge HE-6 (induced by source paper "piecewise testable languages and nondeterministic automata"):
  with members:
    - "on upper and lower bounds on the length of alternating towers"
    - "alternating towers and piecewise testable separators"
    - "separating regular languages by piecewise testable and unambiguous languages"
    - "efficient separability of regular languages by subsequences and suffixes"
    - "piecewise testable tree languages"
    - "around dot depth one"

Connected through hyperedge HE-7 (induced by source paper "relations on words"):
  with members:
    - "testing k binomial equivalence"
    - "a new approach to the 2 regularity of the ell abelian complexity of 2 automatic sequences"
    - "avoiding 2 binomial squares and cubes"
    - "fixed points avoiding abelian k powers"
    - "avoiding three consecutive blocks of the same size and same sum"
    - "on the complexity of the equivalence problem for probabilistic automata"

Connected through hyperedge HE-8 (induced by source paper "the height of piecewise testable languages and the complexity of the logic of subwords"):
  with members:
    - "piecewise testable languages and nondeterministic automata"
    - "on the state complexity of closures and interiors of regular languages with subwords and superwords"
    - "decidability in the logic of subsequences and supersequences"
    - "an approach to computing downward closures"
    - "the height of piecewise testable languages with applications in logical complexity"
    - "finite automata for the sub and superword closure of cfls descriptional and computational complexity"
    - "recompression a simple and powerful technique for word equations"
    - "piecewise testable tree languages"

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)