The document discusses cut-sets and cut-vertices in graphs. It defines a cut-set as a set of edges whose removal disconnects a connected graph. Cut-sets always separate a graph into two disconnected pieces and reduce the graph's rank by one. Theorems are presented regarding the relationship between cut-sets and spanning trees, including that every cut-set must contain at least one branch from every spanning tree. Fundamental cut-sets are also introduced with respect to spanning trees.