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 optimal orientations of cartesian products of graphs (II): complete graphs and even cycles"
  Abstract: For a graph G, let D(G) be the family of strong orientations of G. Define d⇀(G)=min{d(D)/D∈D(G)} and ρ(G)=d⇀(G)−d(G), where d(D) (resp., d(G)) denotes the diameter of the digraph D (resp., graph G). Let G×H denote the cartesian product of the graphs G and H,Kp the complete graph of order p and Cp the cycle of order p. In this paper, we show that ρ(K2×C2m)=2,ρ(Kn×C2m)=1 for n=3,4,5,7, and ρ(Kn×C2m)=0 for most cases otherwise.

Connected through hyperedge HE-1 (induced by source paper "On optimal orientations of cartesian products with a bipartite graph"):
  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