Well you can't :o)

you can.   just get the order right.   share with teh community.  then you can add  names or circles.     

Yes, you can share one way, and then reshare the same post with the other. But I just want to do it all at once.

What I wanted to do is +public and +specific_community/specific_section Maybe that's superfluous, but I don't think so because there are people in the community who don't circle me and so wouldn't have seen the post.

+Julian Bond that's a legitimate request that many people had. The only way to do that, and the correct way according to Google is to first share the post publicly then share the public post with the respective community. This way it gets indexed regardless of community policy.

And the downside is it probably appears twice in your public posts list.

+Julian Bond it doesn't have to, in settings you can turn off community posts from your profile. So I post publicly, but then reshare to communities as necessary. Only the original post is in my profile.

+Christopher Smy Yebbut. That's too aggressively on-off. I want community posts in my profile, I just don't want them to appear twice.

I have no idea what Google's internal data structures are, so have no idea how hard or impossible this is. But from the outside, there should be no difference between a post to circles and a post to a community. So it ought to be possible to just add a community target to the list of circles for that post with only one instance of the post ever existing.

It's only because we can't do that currently that we're trying to solve the problems of duplication. But the duplication should never have appeared in the first place.

It is an issue specifically with Private Communities.  If I want to share a post with a Private community and a select group of individuals, it needs to be 2 steps.  Not the end of the world, but counter-intuitive...