Stefan Ratschan Zhikun She Safety Verification of Hybrid Systems by Constraint Propagation Based Abstraction Refinement. 573-589 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3414&spage=573 2005 conf/hybrid/2005 HSCC db/conf/hybrid/hscc2005.html#RatschanS05