Pattern database
= Pattern database
A table of precomputed exact abstract goal distances used as an <abstraction heuristic>. Retaining a subset of the disks of a <Tower of Hanoi> instance gives a smaller abstract puzzle: moving an ignored disk does not change the abstract state, and moving a retained disk projects to a legal abstract move. Taking maxima of <pattern database> estimates preserves admissibility; summing them requires an additional cost-partition argument.