function sort( r : list ) : list;
	var	head, tail : array[1..M] of list;
		i, j, h : integer;

	begin
	for i:=D downto 1 do begin
		for j:=1 to M do head[j] := nil;
		while r <> nil do begin
			h := charac( i, r^.k );
			if head[h]=nil then head[h] := r
			else	tail[h]^.next := r;
			tail[h] := r;
			r := r^.next;
			end;
		{*** Concatenate lists ***}
		r := nil;
		for j:=M downto 1 do
			if head[j] <> nil then begin
				tail[j]^.next := r;
				r := head[j]
				end
		end;
	sort := r
	end;