human: Given a node-centered hypergraph: <hypergraph>, where nodes represent authors and hyperedges represent groups of authors who co-authored the same paper.

Details of the hypergraph:
Center node: "On an integral operator"
  Abstract: In this paper we derive some criteria for univalence of a general integral operator for analytic functions in the open unit disk.

Connected through hyperedge HE-1 (induced by source paper "On the univalence of an integral operator"):
  with members:
    (none)

Question: Please tell me which research area the center author belongs to. The 4 classes are: Computer science, Mathematics, Engineering, Economics, Psychology, Business. Directly output the class name.

gpt: Mathematics