Christopher Bailey-Kellogg Feng Zhao Qualitative Analysis of Distributed Physical Systems with Applications to Control Synthesis. 232-239 1998 conf/aaai/1998 AAAI/IAAI db/conf/aaai/aaai98.html#Bailey-KelloggZ98 http://www.aaai.org/Library/AAAI/1998/aaai98-032.php