For example, Chaum's blind signatures https://en.wikipedia.org/wiki/Blind_signature https://en.wikipedia.org/wiki/Blind_signature let you create a credential th

For example, Chaum's blind signatures https://en.wikipedia.org/wiki/Blind_signature https://en.wikipedia.org/wiki/Blind_signature let you create a credential that can be anonymously used once but it gets de-anonymized and invalidated if used a second time. This could be applied to age verification so that each credential could only be used once.