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: "Commutative grammars: the complexity of uniform word problems"
  Abstract: Commutative grammars are introduced, and various classes of commutative grammars are defined. The complexity of uniform word problems for commutative grammars is investigated.

Connected through hyperedge HE-1 (induced by source paper "Conjunctive and Boolean grammars: The true general case of the context-free grammars"):
  with members:
    - "Recognizing Two-Sided Contexts in Cubic Time"

Connected through hyperedge HE-2 (induced by source paper "On the equivalence, containment, and covering problems for the regular and context-free languages"):
  with members:
    - "Finding Regular Simple Paths in Graph Databases"
    - "On the complexity of grammar and related problems"

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