note
tilly
It is possible to do it by choosing a number before you see the one in the envelope.<p>
But it is also possible to do it by choosing a number through a mechanical procedure (eg a series of coin flips), in which case it doesn't matter whether you see the number in the envelope first.<p>
However you're exactly right that the <i>method</i> of choosing the random number cannot depend on the number that you see.
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