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 "tree languages defined in first order logic with one quantifier alternation"):
  Abstract: We study tree languages that can be defined in \Delta_2 . These are tree#N#languages definable by a first-order formula whose quantifier prefix is forall#N#exists, and simultaneously by a first-order formula whose quantifier prefix is#N#. For the quantifier free part we consider two signatures, either the#N#descendant relation alone or together with the lexicographical order relation#N#on nodes. We provide an effective characterization of tree and forest languages#N#definable in \Delta_2 . This characterization is in terms of algebraic#N#equations. Over words, the class of word languages definable in \Delta_2 forms#N#a robust class, which was given an effective algebraic characterization by Pin#N#and Weil.

Includes members:
  Member "piecewise testable tree languages":
    also connected through other hyperedges:
      - Hyperedge HE-1 (induced by source paper "partially ordered automata and piecewise testability")
  Member "two way unary temporal logic over trees":
    also connected through other hyperedges:
      - Hyperedge HE-2 (induced by source paper "deciding definability in fo2 h v on trees")

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.FL(Formal Languages and Automata Theory)