On Thu, May 19, 2016 at 04:23:28PM -0600, Nick ODell wrote:
> What if two people create transactions from oupoints  within the same MMR
> tree tip, at the same time?
> 
> For example, I create transaction A plus an MMR proof that MMR tip X will
> become Y.
> 
> On the other side of the planet, someone else creates transaction B, plus
> an MMR proof that tip X will become Z.
> 
> Can a miner who receives A and B put both into a block, without access to
> the outputs that were pruned?

The MMR proofs provided by transactions aren't proofs of *how* the MMR should
be be changd; they're just proofs that the MMR is in a certain state right now.
You're situation is just an example of a double-spend, that miners have to
detect if they don't want to create invalid blocks. Specifically, if I
understand your example correctly, they'd be rejected by the STXO set.

-- 
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