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: "report on the nsf workshop on formal methods for security"
  Abstract: The NSF workshop on Security and Formal Methods, held 19--20 November 2015, brought together developers of formal methods, researchers exploring how to apply formal methods to various kinds of systems, and people familiar with the security problem space.

Connected through hyperedge HE-1 (induced by source paper "new opportunities for integrated formal methods"):
  with members:
    - "model based system assurance using the structured assurance case metamodel"
    - "formal specification and verification of autonomous robotic systems a survey"
    - "fifty years of software engineering or the view from garmisch"
    - "safety practice and its practitioners exploring a diverse profession"
    - "formal methods oversold underused a survey"
    - "robotics and integrated formal methods necessity meets opportunity"
    - "introduction of static quality analysis in small and medium sized software enterprises experiences from technology transfer"
    - "towards a formalization of the unified modeling language"

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.CR(Cryptography and Security)