anchor.diff:  
   (dolist (sudoku (list
                    *royco-minut-soup*
  +                 *metrofrance/694/moyen*
                    *20-minutes/1499/facile*
  -                 *metrofrance/694/moyen*
                    *20-minutes/1501/difficile*
  +                 *20-minutes/1502/expert*
  +                 *metrofrance/696/facile*
  +                 *20-minutes/1505/moyen*
                    ))
     (multiple-value-bind (solutions tries) (sudoku-solver sudoku)
       (terpri)
  
positive.code:                                           (3 x x 8 7 x x x x)
                                            (7 x x x x 4 3 x x)))
  
  
  
  
  
negative.code:                                               (x x x 9 x 6 1 x 5)
                                                (x x x 7 1 x 9 3 x)))
  
  
  (defparameter *20-minutes/1502/expert* #2A((5 7 x x x x x x x)
                                             (x x 8 x x x 1 7 x)
                                             (x 1 x 7 x 4 x 2 8)
                                             (x x 1 x 4 x x 8 5)
                                             (x 5 x x 1 x x 3 x)
                                             (8 6 x x 7 x 4 x x)
                                             (1 4 x 3 x 9 x 6 x)
                                             (x 3 2 x x x 9 x x)
                                             (x x x x x x x 1 3)))
  
  (defparameter *20-minutes/1505/moyen* #2A((1 x 2 x 6 5 9 x x)
                                            (x 4 x 8 x x x x 5)
                                            (x 8 x 1 x x 4 3 6)
                                            (x x 1 9 x x x x x)
                                            (6 5 x x x x x 4 9)
                                            (x x x x x 6 1 x x)
                                            (2 1 3 x x 8 x 5 x)
                                            (8 x x x x 2 x 9 x)
                                            (x x 4 5 7 x 3 x 2)))
  
  (defparameter *metrofrance/694/moyen* #2A((x x 1 2 x x x x 8)
                                            (x x x x 5 1 x x 3)
                                            (x 7 x x x x 6 x 1)
  