问编译错误"4:12:语法错误：。表达式后需要. or运算符“/在prolog中定义动态时出现问题

EN

% Rooms

:- dynamic current_room/1.



room(kitchen).
room(hall).
room(living_room).
room(dinning).


path(kitchen,dinning,n).
path(kitchen,hall2,e).

path(hall,living_room,s).

path(living_room,hall,n).
path(living_room,hall2,s).
path(living_room,dinning,w).

path(dinning,living_room,e).
path(dinning,kitchen,s).

path(hall2,living_room,n).
path(hall2,pantry,s).

path(pantry,hall2,n).


objects(couch).

in_room(living_room,couch).



route(room).

%(current_room,Destination, X).

%asserta(current_room(Destination)).

move(X) :- current_room(Z), path(Z,Y,X), retractall(my_pos(Z)), assert(my_pos(Y)).
n :- move(n).
s :- move(s).
w :- move(w).
e :- move(e).

start :- write('Type n/s/e/w'),nl, asserta(current_room(hall2)).