nostr:nprofile1qqs2js6wu9j76qdjs6lvlsnhrmchqhf4xlg9rvu89zyf3nqq6hygt0spz9mhxue69uhkummnw3ezuamfdejj7qghwaehxw309aex2mrp0yhxummnw3ezucnpdejz7qg4waehxw309aex2mrp0yhxgctdw4eju6t09uygje4n and I (and others) talked about this idea at NostRiga.

Proof of membership. There is a public member list (in this case that's the relay-based-community list) and you want to prove your npub is part of that list without revealing to the verifier which npub u are.

There is a way to do it by using zero-knowledge sets, however my understanding is limited. It should be similar to (and simpler than?) the work nostr:nprofile1qqsxwkuyle67y94tj378gw8w2xw2wa6nwmwlqhddlwnz0z7sztsaw2qppemhxue69uhkummn9ekx7mp0su9alh is doing (tldr; prove that I own UTXOs that exceed the value of X sats, without revealing with ones)