Synthetic Two Stage Ko
Karl Knechtel: I have recently seen positions of this sort crop up fairly often in mid-dan level KGS games.
The groups share a liberty and each has an external simple ko; they do not share the kos. As a result, this plays not like a double ko, but as a two-stage ko determining the status of all inside stones. Having won one ko, neither player can fill, but must instead start the other ko, which then behaves as the next "stage".
With both an eye each and a shared liberty, the position can be seki or mannenko. This is the only construction of two-stage mannenko I am aware of.
It is, presumably, somewhat less likely to be played than an ordinary mannenko, because a two-stage ko starting in the "unfavourable" position is harder to win than a direct ko from the "unfavourable" position. However, one player has the option of capturing an outside ko, and then starting the mannenko in "neutral" position, while opponent gets a gote move in response to the initial capture (as opposed to replying by capturing on the other side to preserve seki). And of course, there is the double-ko potential too (a 4-move cycle exists) - very complicated!
unkx80: The part "one player has the option of capturing an outside ko, and then starting the mannenko in "neutral" position" is wrong --