1. The document discusses minimal spanning trees and the Dijkstra algorithm. A minimal spanning tree connects all points in a network with the minimum total distance. Dijkstra's algorithm finds the shortest paths between a source node and all other nodes in a graph. 2. The minimal spanning tree algorithm connects the nearest unconnected node at each step to build a tree with minimal total distance. Dijkstra's algorithm uses distances between nodes to iteratively build up the shortest path from the source to all other nodes. 3. Both algorithms are useful for problems involving network design and finding optimal connections between locations with given distances, such as telephone networks, road networks, and more.