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: "an np hardness result on the monoid frobenius problem"
  Abstract: The following problem is NP-hard: given a regular expression $E$, decide if $E^*$ is not co-finite.

Connected through hyperedge HE-1 (induced by source paper "the frobenius and factor universality problems of the free monoid on a finite set of words"):
  with members:
    - "on incomplete and synchronizing finite sets"
    - "on non complete sets and restivo s conjecture"
    - "the frobenius problem in a free monoid"

Connected through hyperedge HE-2 (induced by source paper "complexity of the frobenius monoid problem for a finite language"):
  with members:
    - "quotient complexity of regular languages"
    - "the frobenius problem in a free monoid"

Connected through hyperedge HE-3 (induced by source paper "the frobenius problem in a free monoid"):
  with members:
    - "a lower bound on the average case complexity of shellsort"

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.DM(Discrete Mathematics)