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: "a vertex ordering characterization of simple triangle graphs"
  Abstract: Consider two horizontal lines in the plane. A pair of a point on the top line and an interval on the bottom line defines a triangle between two lines. The intersection graph of such triangles is called a simple-triangle graph. This paper shows a vertex ordering characterization of simple-triangle graphs as follows: a graph is a simple-triangle graph if and only if there is a linear ordering of the vertices that contains both an alternating orientation of the graph and a transitive orientation of the complement of the graph.

Connected through hyperedge HE-1 (induced by source paper "linear semiorders and their incomparability graphs"):
  with members:
    - "recognizing simple triangle graphs by restricted 2 chain subgraph cover"
    - "the recognition of simple triangle graphs and of linear interval orders is polynomial"

Connected through hyperedge HE-2 (induced by source paper "recognizing simple triangle graphs by restricted 2 chain subgraph cover"):
  with members:
    - "graph isomorphism completeness for trapezoid graphs"
    - "the recognition of simple triangle graphs and of linear interval orders is polynomial"
    - "extending partial representations of function graphs and permutation graphs"
    - "the recognition of tolerance and bounded tolerance graphs"

Connected through hyperedge HE-3 (induced by source paper "a recognition algorithm for simple triangle graphs"):
  with members:
    - "recognizing simple triangle graphs by restricted 2 chain subgraph cover"
    - "graph isomorphism completeness for trapezoid graphs"
    - "the recognition of simple triangle graphs and of linear interval orders is polynomial"
    - "the recognition of tolerance and bounded tolerance graphs"

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)