+A~vast majority of MST algorithms that we have encountered so far is based on
+the Tarjan's Blue rule (Lemma \ref{bluelemma}). The rule serves to identify
+edges that belong to the MST, while all other edges are left in the process. This
+unfortunately means that the later stages of computation spend most of
+their time on these useless edges. A~notable exception is the randomized
+algorithm of Karger, Klein and Tarjan. It adds an~important ingredient: it uses
+Red rule (Lemma \ref{redlemma}) to filter out edges that are guaranteed to stay
+outside the MST, so that the graphs with which the algorithm works get smaller
+with time.
+