Best way to use Google's hosted jQuery, but fall back to my hosted library on Google fail

Question

What would be a good way to attempt to load the hosted jQuery at Google (or other Google hosted libs), but load my copy of jQuery if the Google attempt fails?

I\'m n

Answer 1

UPDATE:
This answer turned out to be wrong. Please see the comments for the real explanation.

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Most of you question has been answered, but as for the final part:

What would be the danger of both copies coming through?

None really. You'd waste bandwidth, might add some milliseconds downloading a second useless copy, but there's not actual harm if they both come through. You should, of course, avoid this using the techniques mentioned above.