Vitalik: For something to qualify as L2, it must possess security attributes stronger than multi-signature

Ethereum co-founder Vitalik Buterin stated on his social media platform that for me, something eligible to be L2 must have stronger security attributes than multi-signature, even if it's not a comprehensive guarantee like rollup. Validiums meet this requirement, Optimiums can too, but they require rigorous analysis of the exact security gains.