This is a quote from the book "On Zero Confirmation Transactions" by Chris Pacia
...g so, is hardly evidence of unconfirmed transactions being ‘trivially double spent’ or ‘always unsafe’. Yet the opportunity was not missed to push that propaganda on everyone.
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Up to this point we have been considering a network where all miners are using the “first-seen” policy or variations thereof. In such a network, we can
detect double spends and thus prevent almost all fraud attempts as long as our code is up-to-date with the various differences in miner policy.
But opponents of zero confirmations t...