Giusi Castiglione Antonio Restivo Ordering and Convex Polyominoes. 128-139 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3354&spage=128 2004 conf/mcu/2004 MCU db/conf/mcu/mcu2004.html#CastiglioneR04