%query: reach(i,i,i,i).
reach(X,Y,Edges,Not_Visited) :-
	member([X,Y],Edges).
reach(X,Z,Edges,Not_Visited) :-
	member([X,Y],Edges),
        member(Y,Not_Visited),
	delete(Y,Not_Visited,V1),
        reach(Y,Z,Edges,V1).

member(H,[H|L]).
member(X,[H|L]) :- member(X,L).

delete(X,[X|Y],Y).
delete(X,[H|T1],[H|T2]) :- delete(X,T1,T2).


/*TWDESC

read/4. I've not idea what is it, and where I get it from

*/

/*TWDEMO

selected_norms([listlength]).

*/