One of my takeaways: it is not widely understood what is required for federation that is _not_ in the #ActivityPub spec

To federate with other AP instances requires consensus on:

* How to post and load posts (http signatures, not in the spec)
* Account lookups (eg, webfinger)
* What the meaning of a "note" is (overloaded term)
* How to interpret collections and navigate them (not in the spec, or rather it's in the spec but is so broad as to not be useful)
* Reply flows
* JSON-LD

etc

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