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: "comparison of research productivity of italian and norwegian professors and universities"
  Abstract: This is the first ever attempt of application in a country other than Italy of a research efficiency indicator (FSS), to assess and compare the performance of professors and universities, within and between countries. A special attention has been devoted to the presentation of the methodology developed to set up a common field classification scheme of professors, and to overcome the limited availability of comparable input data. Results of the comparison between countries, carried out in the 2011-2015 period, show similar average performances of professors, but noticeable differences in the distributions, whereby Norwegian professors are more concentrated in the tails. Norway shows notable higher performance in Mathematics and Earth and Space Sciences, while Italy in Biomedical Research and Engineering.

Connected through hyperedge HE-1 (induced by source paper "gender disparities in international research collaboration a large scale bibliometric study of 25 000 university professors"):
  with members:
    - "a gender analysis of top scientists collaboration behavior evidence from italy"
    - "academic collaboration rates and citation associations vary substantially between countries and fields"
    - "the collaboration behavior of top scientists"
    - "gender differences in scientific collaborations women are more egalitarian than men"
    - "gender differences in research collaboration"
    - "are researchers that collaborate more at the international level top performers an investigation on the italian university system"
    - "the relationship between scientists research performance and the degree of internationalization of their research"
    - "the contribution of star scientists to overall sex differences in research productivity"

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.DL(Digital Libraries)