Lakshmanan Kuppusamy Kamala Krithivasan On the Relative Expressive Power of Contextual Grammars with Maximal and Depth-First Derivations. 246-260 2009 ICTAC http://dx.doi.org/10.1007/978-3-642-03466-4_16 conf/ictac/2009 db/conf/ictac/ictac2009.html#KuppusamyK09