@maj yes, that's the default for Mastodon, I think. It is only visible to Bob's followers.

@evan I'm going to need a diagram! This is like set theory.

@evan EXACTLY what I imagined.
So, the answer would be visible to the intersect between them.
Of course, how that scales as *those* people reply... there lies the rub.

@evan @maj
So the third item should be "Anyone who are following both Alice and Bob" to be clear. Current form of the item (candidate) can be read "Anyone following whichever Alice or Bob, but not both" as I've confused.

@TomAoki @maj third item is the union.

@maj Dawn's and my answer would be all of Alice's followers. I don't like the intersection answer, because it gets smaller and smaller over time. I think Alice's intent is to have her friends and family have a conversation, like it works on Instagram and Facebook.

@evan @maj that's my answer too, i.e. "Alice's friends", since that's Alice's original intent, a conversation among her friends.

There are advantages to having Bob's reply go to only Alice first, who then fans it out to her followers. For example, it allows full reply controls. It also allows semi-anonymous replies, where Alice can see that Bob sent it but no one else can. This is useful when Bob doesn't want to reveal himself (his profile etc.) to all friends of friends, and it still protects against abuse because Alice still knows it's Bob.

The main disadvantage of routing all replies through Alice's device first is that Alice has to be online for the conversation to continue as it happens. However, Alice could have a trusted (!) server handle the fanning out instead, assuming she doesn't need to manually approve replies.

My social media app FriendSafe routes all replies through the OP (Alice) first. It allows those semi-anonymous replies but doesn't have reply controls now (but it could).