Set TSP problem

In combinatorial optimization, the set TSP, also known as the, group TSP, One-of-a-Set TSP, Multiple Choice TSP or Covering Salesman Problem, is a generalization of the Traveling salesman problem (TSP), whereby it is required to find a shortest tour in a graph which visits all specified disjoint subsets of the vertices of a graph. The ordinary TSP is a special case of the set TSP when all subsets to be visited are singletons. Therefore the set TSP is also NP-hard.