Martin Kappes On the Relationship Between Multiple Brackets and Selector Languages in Bracketed Contextual Grammars. 229-239 2005 64 Fundam. Inform. 1-4 http://iospress.metapress.com/openurl.asp?genre=article&issn=0169-2968&volume=64&issue=1&spage=229 db/journals/fuin/fuin64.html#Kappes05