Philippe Balbiani Valentin Goranko Ruaan Kellerman Dimiter Vakarelov Logical Theories for Fragments of Elementary Geometry. 343-428 2007 Handbook of Spatial Logics http://dx.doi.org/10.1007/978-1-4020-5587-4_7 reference/spatial/2007 db/reference/spatial/spatial2007.html#BalbianiGKV07