5#table path/2.
    6
    7edge(1,2).
    8edge(2,3) :- not edge(2,4).
    9edge(2,4) :- not edge(2,3).
   10
   11
   12path(X,Y) :-
   13    edge(X,Y).
   14path(X,Y) :-
   15    path(X,Z),
   16    edge(Z,Y).
   17
   18
   19?- path(X,Y).