Walaa Aly Seiichi Uchida Akio Fujiyoshi Masakazu Suzuki Statistical Classification of Spatial Relationships among Mathematical Symbols. 1350-1354 2009 ICDAR http://dx.doi.org/10.1109/ICDAR.2009.90 conf/icdar/2009 db/conf/icdar/icdar2009.html#AlyUFS09