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: "a hierarchy of tractable subsets for computing stable models"
  Abstract: Finding the stable models of a knowledge base is a significant computational problem in artificial intelligence. This task is at the computational heart of truth maintenance systems, autoepistemic logic, and default logic. Unfortunately, it is NP-hard. In this paper we present a hierarchy of classes of knowledge bases, Omega_1,Omega_2,..., with the following properties: first, Omega_1 is the class of all stratified knowledge bases; second, if a knowledge base Pi is in Omega_k, then Pi has at most k stable models, and all of them may be found in time O(lnk), where l is the length of the knowledge base and n the number of atoms in Pi; third, for an arbitrary knowledge base Pi, we can find the minimum k such that Pi belongs to Omega_k in time polynomial in the size of Pi; and, last, where K is the class of all knowledge bases, it is the case that union{i=1 to infty} Omega_i = K, that is, every knowledge base belongs to some class in the hierarchy.

Connected through hyperedge HE-1 (induced by source paper "a paraconsistent asp like language with tractable model generation"):
  with members:
    - "answer set solving with bounded treewidth revisited"
    - "backdoors to tractable answer set programming"
    - "logical foundations and complexity of 4ql a query language with unrestricted negation"
    - "the dlv system for knowledge representation and reasoning"

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"
    - "digraph complexity measures and applications in formal language theory"
    - "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"

Connected through hyperedge HE-3 (induced by source paper "backdoors to tractable answer set programming"):
  with members:
    - "guarantees and limits of preprocessing in constraint satisfaction and reasoning"
    - "the parameterized complexity of reasoning problems beyond np"
    - "backdoors to normality for disjunctive logic programs"
    - "numvc an efficient local search algorithm for minimum vertex cover"
    - "backdoors to abduction"
    - "the good the bad and the odd cycles in answer set programs"
    - "strong backdoors to bounded treewidth sat"
    - "strong backdoors to nested satisfiability"

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.AI(Artificial Intelligence)