Connectivity in a graph.
Source: The Art of Prolog
Program source code: graph_connections.pl
/* connected(X,Y) :- Node X is connected to node Y in the graph defined by edge/2. */ connected(X,Y) :- connected(X,Y,[X]). connected(X,X,Visited). connected(X,Y,Visited) :- edge(X,N), not member(N,Visited), connected(N,Y,[N|Visited]). % Program 14.10: Connectivity in a graph