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

star(Commands) :-
	collect_stars(Commands,Stars),
	Stars = [star(StartCol,StartLine0)|RestStars],
	max_line(RestStars,StartLine0,StartLine),
	write_stars(Stars,StartLine,StartCol).

write_stars([],_,_).
write_stars(Lines,StartLine,StartCol) :-
	Lines = [_|_],
	write1line(Lines,StartLine,StartCol),
	findall(star(A,B),(member(star(A,B),Lines),
			   B \== StartLine), RestLines),
	StartLine1 is StartLine - 1,
	write_stars(RestLines,StartLine1,StartCol).

write1line(Lines,StartLine,StartCol) :-
	findall(Col,member(star(Col,StartLine),Lines),Cols),
	sort(Cols,ColsS),
	writecols(ColsS,StartCol),
	nl.

writecols([],_).
writecols([X|R],Col) :-
	Col1 is Col + 1,
	( Col == X ->
	    write('*'),
	    writecols(R,Col1)
	;
	    write(' '),
	    writecols([X|R],Col1)
	).