A * minimum spanning tree*
is a subgraph of a given undirected graph,
containing all the nodes and a subset of the arcs, such that:

- All nodes are connected.
- The resulting graph is a tree, i.e. there are no cycles.
- The sum of weights on the remaining arcs is as low as possible.

** Example:** Connect a set of locations to the Internet using
a minimum length of cable.

The minimum spanning tree may not be unique, but all MST's will have the same total cost of arcs.