Jan Broersen Julien Brunel 'What I Fail to Do Today, I Have to Do Tomorrow': A Logical Study of the Propagation of Obligations. 82-99 2007 CLIMA VIII http://dx.doi.org/10.1007/978-3-540-88833-8_5 conf/clima/2007 db/conf/clima/clima2007.html#BroersenB07