:- use_module(library(lists), [member/2]).

warp(End) :-
        Explored = [],
        Current = start,
        once(explore(Current,Explored,End)).

explore(Current,Explored,End) :-
        directions(Directions),
        member(Direction,Directions),
        move(Direction,NewPoint),
        (
	  \+ member(NewPoint,Explored),
	  ( at_warp(Direction,Current) ->
	      End = NewPoint
	  ;
	      explore(NewPoint,[Current|Explored],End)
	  )
        ;
	  goback(Direction),
	  fail
        ).

goback(Dir) :-
        oppositedir(Dir,Opposite),
        move(Opposite,_).

at_warp(Dir,Current) :-
        oppositedir(Dir,Opposite),
        directions(Dirs),
        once(member(Opposite,Dirs)),
        move(Opposite,NewCurrent),
        move(Dir,_),
        Current == NewCurrent,
        !,
	fail.
at_warp(_,_).

oppositedir(south,north).
oppositedir(north,south).
oppositedir(east,west).
oppositedir(west,east).