:- use_module(library(lists), [append/3, member/2]).

loops(Loops) :-
	findall(arrow(A,B),arrow(A,B),AllArrows),
	findloops(AllArrows,[],Loops) .

findloops([],    AllLoops,AllLoops).
findloops(Arrows,AccLoops,AllLoops) :-
	Arrows = [arrow(Start,_)|_],
	findall([Start|Path],
		path(Start,Start,Arrows,[],Path),LoopsFromStart),
	append(LoopsFromStart,AccLoops,NewAccLoops),
	delete_node(Arrows,Start,RestArrows),
	findloops(RestArrows,NewAccLoops,AllLoops) .

path(Start,Current,Arrows,Visited,Loop) :-
	member(arrow(Current,Next),Arrows),
	\+ member(Next,Visited),
	Loop = [Next|RestLoop],
	( Next == Start ->
	    RestLoop = []
	;
	    path(Start,Next,Arrows,[Next|Visited],RestLoop)
	).

delete_node(   [],   _, []).
delete_node([A|As],Node,Arrows) :-
	( (A = arrow(Node,_) ; A = arrow(_,Node)) ->
	    delete_node(As,Node,Arrows)
	;
	    Arrows = [A|RestArrows],
	    delete_node(As,Node,RestArrows)
	).