0-conf works and Satoshi explicitly said so. Nodes are to discard the second (double spend) transaction they see automatically! Only double spends that occur in the same second need a conf with PoW to be sure which transaction is final.

https://i.imgur.com/j4eTqaB.png

Source: https://www.mail-archive.com/cryptography@metzdowd.com/msg09986.html

0-conf as explained here by Satoshi (and is part of the original Bitcoin) is ESSENTIAL for Bitcoin to work as p2p electronic CASH.

The RBF feature has destroyed 0-conf on BTC , and so BTC is not Bitcoin! I can only conclude BCH is Bitcoin is BTC is Segwitcoin with RBF, BTC is no longer p2p electronic cash and cannot be due to RBF.

For those that don’t know: RBF is a feature on BTC added later (years after Satoshi left) that allows anyone to double spend their transaction before it gets confirmed. It was not part of the software released by Satoshi.

submitted by /u/Brilliant_Wall_9158
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source https://www.reddit.com/r/btc/comments/l3qb3d/0conf_works_and_satoshi_explicitly_said_so_nodes/