Satoshi Kobayashi Takashi Yokomori Yasubumi Sakakibara An Algorithm for Testing Structure Freeness of Biomolecular Sequences. 266-277 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2950&spage=266 2004 conf/birthday/2004head Aspects of Molecular Computing db/conf/birthday/head2004.html#KobayashiYS04