In a backward chaining system, you start with some hypothesis (or goal) you are trying to prove, and keep looking for rules that would allow you to conclude that hypothesis, perhaps setting new sub-goals to prove as you go.

The traveling salesman problem involves n cities with paths connecting the cities. The time taken for traversing through all the cities, without knowing in advance the length of a minimum tour, is ___________

To eliminate the inaccuracy problem in planning problem or partial order planning problem we can use ___________________ data structure/s.