Getting Query Metrics

Is there any way to ask GProlog "how hard" it worked to satisfy a
query?  I've got a really simple Sudoku solver and I've been testing
it with various puzzles.  But I'd like to develop an objective notion
of "how hard" a given puzzle is.

Thanks in advance,
Bill

-- 
Bill Woessner

The problem with eating German food is that, an hour later, you're
hungry for power.