% rewrite('X',[['X','X','X'],['X',0,'X'],['X','X','X']]).
% rewrite(0,[[0,0,0],[0,0,0],[0,0,0]]).

%?- carpet(3).

rewrite('X',[['X','X','X'],[0,'X',0],['X','X','X']]).
rewrite(0,[[0,0,0],[0,0,0],[0,0,0]]).

carpet(I) :-
	carpet(I, C),
	phrase(carpet(C), L),
	format(L).

carpet([]) --> [].
carpet([A|As]) -->
	carpet_line(A),
	"\n",
	carpet(As).

carpet_line([]) --> [].
carpet_line([A|As]) -->
	carpet_dot(A),
	carpet_line(As).

carpet_dot(0) --> " ".
carpet_dot('X') --> "X".

carpet(0, [['X']]).
carpet(I, C) :-
        I > 0,
	I0 is I - 1,
	carpet(I0, C0),
	carpet_rewritten(C0, C).
	

carpet_rewritten([], []).
carpet_rewritten([A|As], C) :-
	line_rewritten(A, B),
	carpet_rewritten(As, Bs),
	append(B, Bs, C).
	

block_append(A, [], A).
block_append([A|As], [B|Bs], [C|Cs]) :-
	append(A, B, C),
	block_append(As, Bs, Cs).
	

line_rewritten([], []).
line_rewritten([A|As], Rs) :-
	rewrite(A, Bs),
	line_rewritten(As, Cs),
	block_append(Bs, Cs, Rs).