Zhongjie Li Jianping Wu Xia Yin Testing Multi Input/Output Transition System with All-Observer. 95-111 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2978&spage=95 2004 conf/pts/2004 TestCom db/conf/pts/testcom2004.html#LiWY04