Life In 19x19

In this position: http://eidogo.com/#2Ctomyl2:0,52

White has just invaded an area where there were formerly just Black stones.

So, the question becomes: how does Black punish White for this move.

As you can see (http://eidogo.com/#2Ctomyl2:0,53) I played O5 to separate the single stone from the floating White group on the right side.

I wouldn't call that an invasion. Looks more like some combination of mojo building and reduction to me. And why do you think there is a punishment?

Agree, if anything that's a reduction, not an invasion.

Also, it looks like a great move to me, so I wouldn't recommend you attempt to punish it.

If you can't come up with a clear punishment, it's best to assume it's a reasonable move and proceed accordingly. The strategy of assuming it's wrong and trying to punish it usually doesn't turn out well.

On short analysis, black seems pretty much behind so this looks good. But I would be very concerned about future of B's 2 lower side stones... Maybe try to make shape there somehow..