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 existential theory of equations with rational constraints in free groups is pspace complete"
  Abstract: It is known that the existential theory of equations in free groups is decidable. This is a famous result of Makanin. On the other hand it has been shown that the scheme of his algorithm is not primitive recursive. In this paper we present an algorithm that works in polynomial space, even in the more general setting where each variable has a rational constraint, that is, the solution has to respect a specification given by a regular word language. Our main result states that the existential theory of equations in free groups with rational constraints is PSPACE-complete. We obtain this result as a corollary of the corresponding statement about free monoids with involution.

Connected through hyperedge HE-1 (induced by source paper "word equations in linear space"):
  with members:
    - "solutions of word equations over partially commutative structures"
    - "recompression a simple and powerful technique for word equations"

Connected through hyperedge HE-2 (induced by source paper "solutions of word equations over partially commutative structures"):
  with members:
    - "more than 1700 years of word equations"
    - "recompression a simple and powerful technique for word equations"

Connected through hyperedge HE-3 (induced by source paper "stochastic parity games on lossy channel systems"):
  with members:
    - "solving stochastic b uchi games on infinite arenas with a finite attractor"
    - "recursive concurrent stochastic games"
    - "verifying nondeterministic probabilistic channel systems against ω regular linear time properties"
    - "decisive markov chains"

Connected through hyperedge HE-4 (induced by source paper "model checking parameterized asynchronous shared memory systems"):
  with members:
    - "parameterized verification of asynchronous shared memory systems"
    - "parameterised pushdown systems with non atomic writes"
    - "the computational power of population protocols"

Connected through hyperedge HE-5 (induced by source paper "solution sets for equations over free groups are edt0l languages icalp 2015 version"):
  with members:
    - "finding all solutions of equations in free groups and monoids with involution"
    - "recompression a simple and powerful technique for word equations"

Connected through hyperedge HE-6 (induced by source paper "more than 1700 years of word equations"):
  with members:
    - "finding all solutions of equations in free groups and monoids with involution"
    - "recompression a simple and powerful technique for word equations"

Connected through hyperedge HE-7 (induced by source paper "finding all solutions of equations in free groups and monoids with involution"):
  with members:
    - "recompression a simple and powerful technique for word equations"

Connected through hyperedge HE-8 (induced by source paper "context unification is in pspace"):
  with members:
    - "approximation of grammar based compression via recompression"
    - "approximation of smallest linear tree grammar"
    - "one variable word equations in linear time"
    - "recompression a simple and powerful technique for word equations"
    - "faster fully compressed pattern matching by recompression"

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.DS(Data Structures and Algorithms)