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