Prolog MAZE中没有实现

正如我在以前的评论说，问题是，get/3在预定义的谓语library(pce)。修改代码很简单：

door(a,b).
door(b,c).
door(c,d).
door(d,e).

myget(X,X,A,P) :-
    reverse(A,P),
    !.
myget(X,Y,A,P) :-
   once(door(X,Z);door(Z,X)),
   not(member(Z,A)),
   format('I am in room ~w.~n', Z),
   myget(Z,Y,[Z|A],P).

查询：

?- myget(a,e,[a],P).
I am in room b.
I am in room c.
I am in room d.
I am in room e.
P = [a, b, c, d, e].