Is "proven" very old -fashioned?

I occasionally see the participle "proven" in mathematical texts, instead of "proved".
Of course I realize that this a deliberate archaism, but I wanted to know if this is still used in books or articles in the USA, and whether a young American would find the form proven odd in 2012.

(I'm asking because I have a not completely finished project for an article that would end with: we have thus proven that the zeros of the zeta function are on the line...)

Solution 1:

Some folks use proven in both the past participle and adjective alike, while others reserve that form to adjectival use and instead use proved only as the verb. Here’s such a distinction:

• He hadn’t yet proved it.
• Is that a proven fact?

I don’t think that either would raise an eyebrow. Or rather, you could alternately use proven in the first case above, but you could not use proved in the second one. At least, that’s what my ear tells me.

Also, I believe the verdict in Scots law is not proven, not not proved.

Edit

As of 2007, the OED3 reports of proven adj.:

This is the usual form in Scottish English (as opposed to proved adj.), and also the preferred form in current North American English. It is now also more frequent than proved adj. in British English.

Its tale under prove v. is much, much longer; I can give only an excerpt here.

Pronunciation: Brit. /pruːv/, U.S. /pruv/
Inflections: Past participle proved, proven.

The past participle proven, originally Scots and the usual form in Scottish English, developed from the β forms by analogy with strong verbs like cloven, past participle of cleave v.¹, woven, past participle of weave v.¹ It is at least as common as proved in current North American English. It is also spreading into other varieties of English, in which the highest proportion of occurrences appears to occur in the past and perfect passive. Compare proven adj., proved adj.

So I really do not think that proven should be considered a deliberate archaism, insofar as in some parts of English it has always had a strong presence, and it seems now to be spreading even to regions where it previously did not hold sway. At least that’s my reading of the OED note above.

Solution 2:

proved, proven. (copypasted)

"The two forms relate to two different verbs derived from Old French prover (ultimately from Latin probare). In standard BrE, proved is the normal past tense and past participle of the verb prove (They proved their point / Their point was proved). Proven survived as a past participle in dialect use and is current in the Scottish legal term not proven (usually pronounced proh-ven) and occasionally in general use in Britain generally (pronounced proo-ven), especially in attributive position (i.e. before a noun):

His love of precise dates and proven facts—N. Shakespeare, 1989.

In AmE, proven is at least as common as proved both as a past tense *[? - Alex B.]*and as a past participle."

"proved" Pocket Fowler's Modern English Usage. Ed. Robert Allen. Oxford University Press, 2008. Oxford Reference Online. Oxford University Press.