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: "Polynomial algorithms for graph isomorphism and chromatic index on partial k -trees"
  Abstract: In this paper we show that Graph Isomorphism and Chromatic Index are solvable in polynomial time when restricted to the class of graphs with treewidth ≤k (k a constant) (or equivalently, the class of partial k-trees). Also, we show that there exist algorithms that find tree-decompositions with treewidth ≤k of graphs with treewidth ≤k, in O(n3) time, (k constant).

Connected through hyperedge HE-1 (induced by source paper "NC-Algorithms for Graphs with Small Treewidth"):
  with members:
    (none)

Connected through hyperedge HE-2 (induced by source paper "The Computational Structure of Monotone Monadic SNP and Constraint Satisfaction: A Study through Datalog and Group Theory"):
  with members:
    - "A dichotomy theorem for constraint satisfaction problems on a 3-element set"
    - "Constraint Satisfaction Problems around Skolem Arithmetic."
    - "A Decidable Dichotomy Theorem on Directed Graph Homomorphisms with Non-negative Weights"

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