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: "on packing colorings of distance graphs"
  Abstract: The packing chromatic number@g"@r(G) of a graph G is the least integer k for which there exists a mapping f from V(G) to {1,2,...,k} such that any two vertices of color i are at a distance of at least i+1. This paper studies the packing chromatic number of infinite distance graphs G(Z,D), i.e. graphs with the set Z of integers as vertex set, with two distinct vertices i,j@?Z being adjacent if and only if |i-j|@?D. We present lower and upper bounds for @g"@r(G(Z,D)), showing that for finite D, the packing chromatic number is finite. Our main result concerns distance graphs with D={1,t} for which we prove some upper bounds on their packing chromatic numbers, the smaller ones being for t>=447: @g"@r(G(Z,{1,t}))@?40 if t is odd and @g"@r(G(Z,{1,t}))@?81 if t is even.

Connected through hyperedge HE-1 (induced by source paper "on packing chromatic number of subcubic outerplanar graphs"):
  with members:
    - "s packing colorings of cubic graphs"
    - "the packing chromatic number of the square lattice is at least 12"

Connected through hyperedge HE-2 (induced by source paper "packing coloring of undirected and oriented generalized theta graphs"):
  with members:
    - "dichotomies properties on computational complexity of s packing coloring problems"
    - "packing chromatic number of distance graphs"
    - "the packing chromatic number of the square lattice is at least 12"

Connected through hyperedge HE-3 (induced by source paper "subdivision into i packings and s packing chromatic number of some lattices"):
  with members:
    - "dichotomies properties on computational complexity of s packing coloring problems"
    - "the packing chromatic number of the square lattice is at least 12"

Connected through hyperedge HE-4 (induced by source paper "packing chromatic number of distance graphs"):
  with members:
    - "the packing chromatic number of the square lattice is at least 12"

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)