Limin Xiang Kazuo Ushijima Yuichi Asahiro Coding k-ary Trees for Efficient Loopless Generation in Lexicographic Order. 396-403 2002 conf/itcc/2002 ITCC http://csdl.computer.org/comp/proceedings/itcc/2002/1506/00/15060396abs.htm db/conf/itcc/itcc2002.html#XiangUA02