Problem of the Week 1100
This unusual type of Sudoku has no numbers given; the usual rules apply (digits from 1 to 9, no two the same in each row, column, or 3×3 subsquare). The small > and < signs indicate which square has the larger number; thus the entry in the upper left is smaller than its right neighbor and larger than its lower neighbor.
As an aid, any square that is smaller than all its neighbors is colored blue; any square that is larger than all its neighbors is colored pink.
Source: Philip Riley and Laura Taalman, authors of the nice book, Color Sudoku, published by Sterling and available at Barnes & Noble bookstores and Amazon.com. Their puzzle enterprise is known as Brainfreeze Puzzles.
© Copyright 2008 Stan Wagon. Reproduced with permission.