Double brackets

[Anders Grusell]

Hi, 
Hope this question is not off-topic, but I cant seem to find anything 
regarding this in the documentation or on the web.
I want to get double square brackets of the type found in this PDF-document:
http://citeseer.nj.nec.com/cache/papers2/cs/529/ftp:zSzzSzftp.diku.dkzSzdikuzSzsemanticszSzpaperszSzD-229.pdf/efficient-multi-level-generating.pdf
(In section 2.1 for example)

Thanks,
Anders G