Which "assumptions" made about the state space are Russell and Norvig referring to in their book? I am reading the cornerstone book, &quot;Artificial Intelligence, A Modern Approach&quot; by Stuart Russel, and Peter Norvig, and there is a passage in the book on page 98:

The complexity results depend very strongly on the assumptions made
about the state space. The simplest model studied is a state space
that has a single goal and is essentially a tree with reversible
actions. (The 8-puzzle satisfies the first and third of these
assumptions.)

What are the &quot;assumptions&quot; in that context?
The complexity results depend very strongly on the assumptions made about the state space. The simplest model studied is a state space that has a single goal and is essentially a tree with reversible actions. 


The assumptions are the following: 



  The simplest model studied is a state space


  that has a single goal 


  and is essentially a tree with reversible actions.