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 the μ-calculus over transitive and finite transitive frames"
  Abstract: We prove that the modal @m-calculus collapses to first order logic over the class of finite transitive frames. The proof is obtained by using some byproducts of a new proof of the collapse of the @m-calculus to the alternation free fragment over the class of transitive frames. Moreover, we prove that the modal @m-calculus is Buchi and co-Buchi definable over the class of all models where, in a strongly connected component, vertexes are distinguishable by means of the propositions they satisfy.

Connected through hyperedge HE-1 (induced by source paper "Modal characterisation theorems over special classes of frames"):
  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