virtual groups
A useful way of approaching framework theory is to think of possible invasions as 'virtual groups' - groups that exist in your head rather than (yet) on the board.
So virtual groups have a life cycle:
- any real framework (not secure territory) has some virtual group or groups inside it;
- an actual invasion creates a weak group from a virtual group;
- virtual groups may live, if an invasion lives;
- virtual groups may die, if (a) the framework is reinforced in such a way as to prevent an effective invasion, or (b) the invasion takes place but the group created dies (mochikomi).
If a framework is turned into territory, that means all the virtual groups inside it are now dead. Often the final play consolidating the territory is very efficient; the translation of that in virtual group terms may be that it kills two virtual groups at once.
For example Black plays 1 (the iron pillar) in the hope of reducing to nothing White's aji to live around a, and around b.
The terminology of virtual groups is just a way of discussing aji for life. It is quite graphic and suggestive. I learned it in seminars of Matthew Macfadyen. Charles Matthews