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: "enumeration and structure of trapezoidal words"
  Abstract: Trapezoidal words are words having at most n+1 distinct factors of length n for every n>=0. They therefore encompass finite Sturmian words. We give combinatorial characterizations of trapezoidal words and exhibit a formula for their enumeration. We then separate trapezoidal words into two disjoint classes: open and closed. A trapezoidal word is closed if it has a factor that occurs only as a prefix and as a suffix; otherwise it is open. We investigate open and closed trapezoidal words, in relation with their special factors. We prove that Sturmian palindromes are closed trapezoidal words and that a closed trapezoidal word is a Sturmian palindrome if and only if its longest repeated prefix is a palindrome. We also define a new class of words, semicentral words, and show that they are characterized by the property that they can be written as uxyu, for a central word u and two different letters x,y. Finally, we investigate the prefixes of the Fibonacci word with respect to the property of being open or closed trapezoidal words, and show that the sequence of open and closed prefixes of the Fibonacci word follows the Fibonacci sequence.

Connected through hyperedge HE-1 (induced by source paper "characteristic parameters and special trapezoidal words"):
  with members:
    - "the sequence of open and closed prefixes of a sturmian word"
    - "on the structure of bispecial sturmian words"

Connected through hyperedge HE-2 (induced by source paper "the sequence of open and closed prefixes of a sturmian word"):
  with members:
    - "factorizations of the fibonacci infinite word"
    - "on the structure of bispecial sturmian words"
    - "on the number of closed factors in a word"
    - "some extremal properties of the fibonacci word"
    - "a classification of trapezoidal words"

Connected through hyperedge HE-3 (induced by source paper "closed palindromic rich privileged trapezoidal and balanced words in automatic sequences"):
  with members:
    - "remarks on privileged words"
    - "on the number of closed factors in a word"
    - "on the number of unbordered factors"
    - "subword complexity and k synchronization"
    - "enumeration and decidable properties of automatic sequences"

Connected through hyperedge HE-4 (induced by source paper "on the structure of bispecial sturmian words"):
  with members:
    - "a characterization of bispecial sturmian words"
    - "uniformly balanced words with linear complexity and prescribed letter frequencies"

Connected through hyperedge HE-5 (induced by source paper "on the number of closed factors in a word"):
  with members:
    - "a classification of trapezoidal words"

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)