human: Given a hyperedge-centered hypergraph: <hypergraph>, where the center hyperedge groups authors who co-authored the same paper.

Details of the hypergraph:
Center hyperedge (induced by source paper "Algorithm for Finding k-Vertex Out-trees and Its Application to k-Internal Out-branching Problem"):
  Abstract: An  out-tree   T  is an oriented tree with exactly one vertex of in-degree zero and a vertex  x  of  T  is called  internal  if its out-degree is positive. We design randomized and deterministic algorithms for deciding whether an input digraph contains a subgraph isomorphic to a given out-tree with  k  vertices. Both algorithms run in  O  *(5.704  k  ) time. We apply the deterministic algorithm to obtain an algorithm of runtime  O  *( c   k  ), where  c  is a constant, for deciding whether an input digraph contains a spanning out-tree with at least  k  internal vertices. This answers in affirmative a question of Gutin, Razgon and Kim (Proc. AAIM'08).

Includes members:
  Member "Algorithm for finding k-vertex out-trees and its application to k-internal out-branching problem":
    also connected through other hyperedges:
      (none)

Question: Please tell me which research area the co-authored paper (i.e., the source paper of the center hyperedge) belongs to. The 4 classes are: Computer science, Mathematics, Engineering, Economics, Psychology, Business. Directly output the class name.

gpt: Mathematics