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 improved upper bound on the integrality ratio for the s t path tsp"
  Abstract: We give an improved analysis of the best-of-many Christofides algorithm with lonely edge deletion, which was proposed by Seb\H{o} and van Zuylen [2016]. This implies an improved upper bound on the integrality ratio of the standard LP relaxation for the $s$-$t$-path TSP.

Connected through hyperedge HE-1 (induced by source paper "beating the integrality ratio for s t tours in graphs"):
  with members:
    - "a 1 5 approximation for path tsp"
    - "a constant factor approximation algorithm for the asymmetric traveling salesman problem"
    - "approaching frac 3 2 for the s t path tsp"
    - "approximation hardness of graphic tsp on cubic graphs"
    - "improving christofides algorithm for the s t path tsp"

Connected through hyperedge HE-2 (induced by source paper "approaching frac 3 2 for the s t path tsp"):
  with members:
    - "a 1 5 approximation for path tsp"
    - "layers and matroids for the traveling salesman s paths"
    - "better s t tours by gao trees"
    - "reassembling trees for the traveling salesman"
    - "improving christofides algorithm for the s t path tsp"

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)