- INSTANCE: Graph , edge cost , and sets , also called groups.
- SOLUTION: A tree in which contains at least one terminal from every group
- COST FUNCTION: .
- OBJECTIVE: Minimize.
*Approx.:*Approximable within . Approximable within if is a tree [53], [40].*Hardness:*Not approximable within unless NP admits quasipolynomial-time Las Vegas algorithm [61].*Comment:*Approximable within when the graph is planar and each group is the set of nodes on a face [40].

2015-04-27 Revision: 288 PDF version