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 small diameter"
  Abstract: A graph that contains a spanning tree of diameter at most $t$ clearly admits a tree $t$-spanner, since a tree $t$-spanner of a graph $G$ is a sub tree of $G$ such that the distance between pairs of vertices in the tree is at most $t$ times their distance in $G$. In this paper, graphs that admit a tree $t$-spanner of diameter at most $t+1$ are studied. For $t$ equal to 1 or 2 the problem has been solved. For $t=3$ we present an algorithm that determines if a graph admits a tree 3-spanner of diameter at most 4. For $t\geq4$ it is proved that it is an NP-complete problem to decide whether a graph admits a tree $t$-spanner of diameter at most $t+1$.

Connected through hyperedge HE-1 (induced by source paper "tree spanners of bounded degree graphs"):
  with members:
    - "on approximating tree spanners that are breadth first search trees"
    - "tree 3 spanners of diameter at most 5"
    - "tree t spanners in outerplanar graphs via supply demand partition"
    - "nearly linear time algorithms for graph partitioning graph sparsification and solving linear systems"

Connected through hyperedge HE-2 (induced by source paper "on approximating tree spanners that are breadth first search trees"):
  with members:
    - "tree spanners of bounded degree graphs"
    - "nearly linear time algorithms for graph partitioning graph sparsification and solving linear systems"

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