Crista was concerned with at least two things in her messages:

1. "Surprise" paths when we have positive information in strategies: 
   This problem is solved in my mind and I think also 
   in Boaz' mind by making strategies WYSIWYG.

2. Premature termination
   Boaz was pointing out that he and Mitch have similar concerns.
   Boaz actually proposes a framework for solving it
   (amortizing the lookahead over the construction actions).
   Boaz will summarize the approach on Monday and then we 
   can have a discussion.

   I think that the curious, optimistic traversal approach which
   we have now is the right one (for efficiency reasons). If we don't
   know whether we can get to a node, we pack the information into a visitor
   and act on it only when we got there. This solves the undo problem.

-- Karl