Patrizia Asirelli Maurice H. ter Beek Stefania Gnesi Alessandro Fantechi Deontic Logics for Modeling Behavioural Variability. 71-76 2009 VaMoS http://www.vamos-workshop.net/proceedings/VaMoS_2009_Proceedings.pdf conf/vamos/2009 db/conf/vamos/vamos2009.html#AsirelliBGF09