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: "digraph complexity measures and applications in formal language theory"
  Abstract: We investigate structural complexity measures on digraphs, in particular the cycle rank. This concept is intimately related to a classical topic in formal language theory, namely the star height of regular languages. We explore this connection, and obtain several new algorithmic insights regarding both cycle rank and star height. Among other results, we show that computing the cycle rank is NP-complete, even for sparse digraphs of maximum outdegree 2. Notwithstanding, we provide both a polynomial-time approximation algorithm and an exponential-time exact algorithm for this problem. The former algorithm yields an O((log n)^(3/2))- approximation in polynomial time, whereas the latter yields the optimum solution, and runs in time and space O*(1.9129^n) on digraphs of maximum outdegree at most two. Regarding the star height problem, we identify a subclass of the regular languages for which we can precisely determine the computational complexity of the star height problem. Namely, the star height problem for bideterministic languages is NP-complete, and this holds already for binary alphabets. Then we translate the algorithmic results concerning cycle rank to the bideterministic star height problem, thus giving a polynomial-time approximation as well as a reasonably fast exact exponential algorithm for bideterministic star height.

Connected through hyperedge HE-1 (induced by source paper "width parameterizations for knot free vertex deletion on digraphs"):
  with members:
    - "an algorithmic metatheorem for directed treewidth"
    - "subgraphs satisfying mso properties on z topologically orderable digraphs"
    - "are there any good digraph width measures"
    - "the combinatorics of resource sharing"

Connected through hyperedge HE-2 (induced by source paper "clique width and directed width measures for answer set programming"):
  with members:
    - "directed width measures and monotonicity of directed graph searching"
    - "a trichotomy for regular simple path queries on graphs"
    - "backdoors to tractable answer set programming"
    - "trichotomy and dichotomy results on the complexity of reasoning with disjunctive logic programs"
    - "fixed parameter complexity of semantics for logic programs"
    - "a hierarchy of tractable subsets for computing stable models"

Connected through hyperedge HE-3 (induced by source paper "an algorithmic metatheorem for directed treewidth"):
  with members:
    - "subgraphs satisfying mso properties on z topologically orderable digraphs"
    - "are there any good digraph width measures"
    - "on complexity of minimum leaf out branching problem"

Connected through hyperedge HE-4 (induced by source paper "subgraphs satisfying mso properties on z topologically orderable digraphs"):
  with members:
    - "on the parameterized intractability of monadic second order logic"
    - "lower bounds for the complexity of monadic second order logic"
    - "are there any good digraph width measures"

Connected through hyperedge HE-5 (induced by source paper "lifo search on digraphs a searching game for cycle rank"):
  with members:
    - "digraph decompositions and monotonicity in digraph searching"

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)