%	Knowledge	Base
edge(a,b).
edge(b,c).
edge(c,d).
edge(d,a).
edge(d,e).
edge(b,a).

path(X,Y):-
    edge(X,Y), !.
path(X,Y):-
    pathN(X,Y,[]), !.
pathN(X,Y,List):-
    edge(X,Z),
    (   member(Z, List)
    ->  fail
    ;   List2 = [Z|List], pathN(Z,Y, List2)).