Examine the definition of bidirectional search in Chapter search-chapter.
Would bidirectional state-space search be a good idea for planning?
What about bidirectional search in the space of partial-order plans?
Devise a version of partial-order planning in which an action can be added to a plan if its preconditions can be achieved by the effects of actions already in the plan. Explain how to deal with conflicts and ordering constraints. Is the algorithm essentially identical to forward state-space search?