#domain piece(P).
#domain piece(P1).
#domain piece(P2).
#domain piece(P3).
#domain piece(P4).
#domain type(T).
#domain direction(D).
#domain direction(D1).
#domain direction(D2).
#domain direction(D2).

direction(north;south;east;west).

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

type(source).
type(target).
type(blocker).
type(divider).

{ edge(P1,P2,D1) } :-
	P1 != P2,
	output_direction(P1,D1),
	input_direction(P2,D2),
	opposite(D1,D2).

:- edge(P,P1,D), edge(P,P2,D), P1 < P2. % sufficient to check one side of ineq
:- edge(P1,P,D), edge(P2,P,D), P1 < P2.

edge(P1,P2) :- edge(P1,P2,D).

:- edge(P1,P2), tag(P1,source), tag(P2,target).

:- edge(P,P1), not laser_out(P).

laser_out(P) :-	tag(P,source).
laser_out(P) :- tag(P,divider), laser_in(P).

laser_in(P2) :- edge(P1,P2), laser_out(P1).

:- tag(P,target), not laser_in(P).

in_play(P) :- edge(P,_).
in_play(P) :- edge(_,P).
in_play(P) :- tag(P,source).
in_play(P) :- tag(P,target).
in_play(P) :- tag(P,blocker).

fixed(P) :- at(P,X,Y).

#domain split_count(S).
split_count(1..3).
divider_outs(P,S) :- tag(P,divider), S { output_direction(P,Di) :direction(Di) } S.

#hide.
#show edge/3.