the zero-knowledge membership primitive (Ethereum PSE, in production since 2020, v4 in 2024). an identity is a commitment in a group's Merkle tree; a member proves "I belong" and broadcasts a signal — a vote, a report, an attestation — with one nullifier per scope, so each member signals once per context and stays anonymous across all of them. the grammar under anonymous voting, whistleblowing and proof-of-personhood systems at millions-of-users scale
the lesson: identity is membership without a name. belonging proves itself; the nullifier meters participation without identifying the participant. the exact shape a neuron needs to prove karma thresholds or cast a governance signal while the key stays cold