Absent-mindedness occurs when a player, moving along a single path of play, can re-enter an information set visited previously. Detecting this property is valuable for users to:

• Better understand the structure of their game.
• Be warned if using certain concepts and solution algorithms that are incompatible with absent-mindedness.

The existing GameTreeRep::BuildInfosetParents() method already contains the necessary traversal logic to detect this condition.

1. Add a new data member to GameTreeRep: std::set<GameInfoset> m_absentMindedInfosets;
2. Augment the existing BuildInfosetParents() traversal to populate m_absentMindedInfosets that tracks all absent-minded information sets.
3. A new public method, IsAbsentMinded() const, will mirror the logic of IsPerfectRecall(): it will trigger the traversal if needed and then check the state of the new container.