“The payee needs proof that at…
“The payee needs proof that at the time of each transaction, the majority of nodes agreed it was the first received. […] When there are multiple double-spent versions of the same transaction, one and only one will become valid. The receiver of a payment must wait an hour or so before believing that it’s valid. The network will resolve any possible double-spend races by then.”
-- Satoshi Nakamoto (2009)
