
More questions about your code.

3. There seems to be some undocumented abstraction methods:
     -- BS (?? bias-stars ?? the documentation in the file is identical,
               as far as I can tell, to that in "stars".
               What's the difference ??)
     -- SD (?? I have no clue.  Well, looking more closely I see that it
            builds stars with either predecessors or successors, depending
            on the search direction)
     -- SP (progressive stars, I like this idea)
     -- Pc (?? Compress -- the documentation in the file explains this)


4. I am inclined to define a signature for an abstraction method.
   Is there any particular reason why you didn't do this ?

-- rob
     
