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: "tree spanners of bounded degree graphs"
  Abstract: A tree   t     t       -spanner of a graph   G     G        is a spanning tree of   G     G        such that the distance between pairs of vertices in the tree is at most   t     t        times their distance in   G     G       . Deciding tree   t     t       -spanner admissible graphs has been proved to be tractable for   t     t    3        and NP-complete for   t>3     t  >  3       , while the complexity status of this problem is unresolved when   t=3     t  =  3       . For every   t>2     t  >  2        and   b>0     b  >  0       , an efficient dynamic programming algorithm to decide tree   t     t       -spanner admissibility of graphs with vertex degrees less than   b     b        is presented. Only for   t=3     t  =  3       , the algorithm remains efficient, when graphs   G     G        with degrees less than   blog|V(G)|     b  log   |  V   (  G  )   |         are examined.

Connected through hyperedge HE-1 (induced by source paper "on approximating tree spanners that are breadth first search trees"):
  with members:
    - "tree spanners of small diameter"
    - "nearly linear time algorithms for graph partitioning graph sparsification and solving linear systems"

Connected through hyperedge HE-2 (induced by source paper "tree 3 spanners of diameter at most 5"):
  with members:
    - "tree spanners of small diameter"

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)