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: "piecewise testable languages and nondeterministic automata"
  Abstract: A regular language is $k$-piecewise testable if it is a finite boolean combination of languages of the form $\Sigma^* a_1 \Sigma^* \cdots \Sigma^* a_n \Sigma^*$, where $a_i\in\Sigma$ and $0\le n \le k$. Given a DFA $A$ and $k\ge 0$, it is an NL-complete problem to decide whether the language $L(A)$ is piecewise testable and, for $k\ge 4$, it is coNP-complete to decide whether the language $L(A)$ is $k$-piecewise testable. It is known that the depth of the minimal DFA serves as an upper bound on $k$. Namely, if $L(A)$ is piecewise testable, then it is $k$-piecewise testable for $k$ equal to the depth of $A$. In this paper, we show that some form of nondeterminism does not violate this upper bound result. Specifically, we define a class of NFAs, called ptNFAs, that recognize piecewise testable languages and show that the depth of a ptNFA provides an (up to exponentially better) upper bound on $k$ than the minimal DFA. We provide an application of our result, discuss the relationship between $k$-piecewise testability and the depth of NFAs, and study the complexity of $k$-piecewise testability for ptNFAs.

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"
    - "the height of piecewise testable languages and the complexity of the logic of subwords"
    - "on separation by locally testable and locally threshold testable languages"
    - "separating regular languages by piecewise testable and unambiguous languages"

Connected through hyperedge HE-2 (induced by source paper "on shuffle products acyclic automata and piecewise testable languages"):
  with members:
    - "decidability complexity and expressiveness of first order logic over the subword ordering"
    - "the height of piecewise testable languages and the complexity of the logic of subwords"
    - "the height of piecewise testable languages with applications in logical complexity"

Connected through hyperedge HE-3 (induced by source paper "separability by piecewise testable languages is ptime complete"):
  with members:
    - "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"
    - "piecewise testable tree languages"
    - "around dot depth one"

Connected through hyperedge HE-4 (induced by source paper "complexity of universality and related problems for partially ordered nfas"):
  with members:
    - "separating regular languages with two quantifier alternations"
    - "the computational complexity of universality problems for prefixes suffixes factors and subwords of regular languages"

Connected through hyperedge HE-5 (induced by source paper "the height of piecewise testable languages and the complexity of the logic of subwords"):
  with members:
    - "on the state complexity of closures and interiors of regular languages with subwords and superwords"
    - "decidability in the logic of subsequences and supersequences"
    - "on the index of simon s congruence for piecewise testability"
    - "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)