human: Given a hyperedge-centered hypergraph: <hypergraph>, where the center hyperedge is induced by one source paper and its member nodes are the cited papers.

Details of the hypergraph:
Center hyperedge (induced by source paper "better s t tours by gao trees"):
  Abstract: We consider the $s$-$t$-path TSP: given a finite metric space with two elements $s$ and $t$, we look for a path from $s$ to $t$ that contains all the elements and has minimum total distance. We improve the approximation ratio for this problem from 1.599 to 1.566. Like previous algorithms, we solve the natural LP relaxation and represent an optimum solution $x^*$ as a convex combination of spanning trees. Gao showed that there exists a spanning tree in the support of $x^*$ that has only one edge in each narrow cut (i.e., each cut $C$ with $x^*(C)<2$). Our main theorem says that the spanning trees in the convex combination can be chosen such that many of them are such "Gao trees''.

Includes members:
  Member "layers and matroids for the traveling salesman s paths":
    also connected through other hyperedges:
      - Hyperedge HE-1 (induced by source paper "an improved upper bound on the integrality ratio for the s t path tsp")
  Member "an experimental evaluation of the best of many christofides algorithm for the traveling salesman problem":
    also connected through other hyperedges:
      - Hyperedge HE-2 (induced by source paper "fast approximations for metric tsp via linear programming")
  Member "reassembling trees for the traveling salesman":
    also connected through other hyperedges:
      - Hyperedge HE-3 (induced by source paper "reducing path tsp to tsp")
  Member "on the metric s t path traveling salesman problem":
    also connected through other hyperedges:
      - Hyperedge HE-4 (induced by source paper "a 1 5 approximation for path tsp")
  Member "eight fifth approximation for the path tsp":
    also connected through other hyperedges:
      - Hyperedge HE-5 (induced by source paper "constant factor approximation algorithms for parity constrained facility location problems")
  Member "approximating minimum cost connected t joins":
    also connected through other hyperedges:
      - Hyperedge HE-6 (induced by source paper "constant factor approximation algorithms for parity constrained facility location problems")
  Member "improving christofides algorithm for the s t path tsp":
    also connected through other hyperedges:
      - Hyperedge HE-7 (induced by source paper "reducing path tsp to tsp")

Question: Please tell me which class the source paper 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)