% code common to star, similistar and starpalindrome

collect_stars(Commands,Stars) :-
	once(collect_stars(Commands,0,0,UnorderedStars)),
	sort(UnorderedStars,Stars).

collect_stars([]               ,_,_,[]).
collect_stars([up   | Commands],I,J,Stars) :-
	J1 is J + 1,
	collect_stars(Commands,I,J1,Stars).
collect_stars([down | Commands],I,J,Stars) :-
	J1 is J - 1,
	collect_stars(Commands,I,J1,Stars).
collect_stars([left | Commands],I,J,Stars) :-
	I1 is I - 1,
	collect_stars(Commands,I1,J,Stars).
collect_stars([right| Commands],I,J,Stars) :-
	I1 is I + 1,
	collect_stars(Commands,I1,J,Stars).
collect_stars([star | Commands],I,J,[star(I,J)| Stars]) :-
	collect_stars(Commands,I,J,Stars).

max_line([],Max,Max).
max_line([star(_,L)|RestStars],MaxSoFar,Max) :-
	( L > MaxSoFar ->
	    max_line(RestStars,L,Max)
	;
	    max_line(RestStars,MaxSoFar,Max)
	).