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: "the four in a tree problem in triangle free graphs"
  Abstract: The three-in-a-tree algorithm of Chudnovsky and Seymour decides in time O(n 4) whether three given vertices of a graph belong to an induced tree. Here, we study four-in- a-tree for triangle-free graphs. We give a structural answer to the following question: what does a triangle-free graph look like if no induced tree covers four given vertices? Our main result says that any such graph must have the “same structure”, in a sense to be defined precisely, as a square or a cube. We provide an O(nm)-time algorithm that given a triangle-free graph G together with four vertices outputs either an induced tree that contains them or a partition of V(G) certifying that no such tree exists. We prove that the problem of deciding whether there exists a tree T covering the four vertices such that at most one vertex of T has degree at least 3 is NP-complete.

Connected through hyperedge HE-1 (induced by source paper "three in a tree in near linear time"):
  with members:
    - "graph pattern detection hardness for all induced patterns and faster non induced cycles"
    - "a faster algorithm to recognize even hole free graphs"
    - "on the structure of pan even hole free graphs"
    - "powers of tensors and fast matrix multiplication"
    - "detecting an induced net subdivision"
    - "large induced subgraphs via triangulations and cmso"
    - "induced disjoint paths in claw free graphs"
    - "detecting 2 joins faster"

Connected through hyperedge HE-2 (induced by source paper "induced disjoint paths in claw free graphs"):
  with members:
    - "the k in a path problem for claw free graphs"
    - "domination when the stars are out"
    - "finding topological subgraphs is fixed parameter tractable"
    - "the k in a tree problem for graphs of girth at least k"
    - "detecting induced subgraphs"

Connected through hyperedge HE-3 (induced by source paper "the k in a path problem for claw free graphs"):
  with members:
    - "the k in a tree problem for graphs of girth at least k"
    - "detecting induced subgraphs"

Connected through hyperedge HE-4 (induced by source paper "the k in a tree problem for graphs of girth at least k"):
  with members:
    - "detecting induced subgraphs"

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)