[INDOLOGY] dating 'nirvana'

[Howard Resnick]

	First, my apologies for some rudimentary questions, however I am at present sadly distant from any serious Indology library.

	The word 'nirvana' in late Vedic/Hindu literature is regularly taken to confirm a post-Buddha date for that text, as with Bhagavad-gita. Does this term, 'nirvana', occur in any Vedic, or early Hindu Upanisads or other kinds of texts? If so, do we have strong evidence to obviate the circularity of assuming that 'nirvana' in these texts indicates a post-Buddha date, because the term is first used in Buddhism?

	I would be very grateful for any online resources, given my situation. I would also be exceedingly grateful for any brief explanations.

Best to all,
Howard Resnick