4%#table path/2.
    5
    6edge(a,b).
    7edge(b,c).
    8edge(a,d) :- not path(c,d).
    9
   10path(X,Y) :-
   11    edge(X,Y).
   12path(X,Y) :-
   13    edge(X,Z),
   14    path(Z,Y).
   15
   16
   17?- path(a,Y).