human: Given a hyperedge-centered hypergraph: <hypergraph>, where the center hyperedge is induced by one source paper and its member nodes are the cited papers.

Details of the hypergraph:
Center hyperedge (induced by source paper "bisimulation equivalence of first order grammars is ackermann complete"):
  Abstract: Checking whether two pushdown automata with restricted silent actions are weakly bisimilar was shown decidable by Senizergues (1998, 2005). We provide the first known complexity upper bound for this famous problem, in the equivalent setting of first-order grammars. This ACKERMANN upper bound is optimal, and we also show that strong bisimilarity is primitive-recursive when the number of states of the automata is fixed.

Includes members:
  Member "equivalence of pushdown automata via first order grammars":
    also connected through other hyperedges:
      (none)
  Member "complexity hierarchies beyond elementary":
    also connected through other hyperedges:
      - Hyperedge HE-1 (induced by source paper "the ideal approach to computing closed subsets in well quasi orderings")
  Member "branching bisimilarity checking for prs":
    also connected through other hyperedges:
      - Hyperedge HE-2 (induced by source paper "games for bisimulations and abstraction")
  Member "bisimulation equivalence of first order grammars":
    also connected through other hyperedges:
      - Hyperedge HE-3 (induced by source paper "deciding semantic finiteness of pushdown processes and first order grammars w r t bisimulation equivalence")
  Member "complexity bounds for ordinal based termination":
    also connected through other hyperedges:
      - Hyperedge HE-4 (induced by source paper "the ideal approach to computing closed subsets in well quasi orderings")
  Member "bpa bisimilarity is exptime hard":
    also connected through other hyperedges:
      - Hyperedge HE-5 (induced by source paper "expspace hardness of behavioural equivalences of succinct one counter nets")
  Member "beyond language equivalence on visibly pushdown automata":
    also connected through other hyperedges:
      - Hyperedge HE-6 (induced by source paper "expspace hardness of behavioural equivalences of succinct one counter nets")
  Member "the bisimulation problem for equational graphs of finite out degree":
    also connected through other hyperedges:
      - Hyperedge HE-7 (induced by source paper "bisimulation equivalence of first order grammars")

Question: Please tell me which class the source paper 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.LO(Logic in Computer Science)