bos bos ord ord jfk jfk sfo sfo dfw dfw lax lax mia mia ( (bbos bos ord ord jfk sfo jfk sfo dfw dfw lax lax mia (cmia (dfigure examples of reachability in directed graph(aa directed path from bos to lax is highlighted(ba directed cycle (ordmiadfwlaxordis highlightedits vertices induce strongly connected subgraph(cthe subgraph of the vertices and edges reachable from ord is highlighted(dthe removal of the dashed edges results in an acyclic directed graph example perhaps the most talked about graph today is the internetwhich can be viewed as graph whose vertices are computers and whose (undirectededges are communication connections between pairs of computers on the internet the computers and the connections between them in single domainlike wiley comform subgraph of the internet if this subgraph is connectedthen two users on computers in this domain can send email to one another without having their information packets ever leave their domain suppose the edges of this subgraph form spanning tree this implies thatif even single connection goes down (for examplebecause someone pulls communication cable out of the back of computer in this domain)then this subgraph will no longer be connected