July 20, 2002 [LINK]

### Sudoku: ¡Qué tal rompecabeza*!

8 | 1 | 5 | 6 | 7 | 4 | 9 | 2 | 3 |

9 | 4 | 2 | 3 | 8 | 5 | 1 | 7 | 6 |

7 | 3 | 6 | 9 | 1 | 2 | 4 | 5 | 8 |

5 | 7 | 9 | 4 | 6 | 1 | 3 | 8 | 2 |

3 | 6 | 8 | 7 | 2 | 9 | 5 | 4 | 1 |

4 | 2 | 1 | 8 | 5 | 3 | 7 | 6 | 9 |

6 | 9 | 3 | 5 | 4 | 8 | 2 | 1 | 7 |

2 | 8 | 4 | 1 | 3 | 7 | 6 | 9 | 5 |

1 | 5 | 7 | 2 | 9 | 6 | 8 | 3 | 4 |

*Washington Post*began running a new brain teasing puzzle called "Sudoku" on one of their three (!) comics pages a couple weeks ago, bumping aside the crossword puzzle, and I must confess to becoming a semi-avid player. It consists of a 9 x 9 grid divided into nine 3 x 3 grids. Each row, each column, and each 3 x 3 grid consists of the numerals 1 through 9, with none being repeated. Anywhere from one fourth to one half of the numerals are already filled in when you begin (indicated here by bold face type and gray or dull green background), depending on whether you've got a hard, medium, or easy puzzle, providing all the clues you need to deduce all the rest. For example, since you know that one of the cells in the center 3 x 3 grid must be a "1," the "1" shaded greenish on the left side and the "1" shaded greenish on the right side establish that the "1" in the central grid must be in its top row (the fourth row). The "1" shaded greenish on the upper side and the "1" shaded greenish on the lower side establish that the "1" in the central grid cannot be in its upper left or upper middle cell, so it must be in the upper right cell, which is shaded pink. And so on and so forth. You can see examples and tips on the Sudoku Web site, but I prefer to figure out the tricks to solving them on my own. For example, A couple days ago I hit upon a new logical trick: I was stumped because I knew that two separate pairs of cells had to be one of two numbers, but there wasn't enough information to decided which was which. That was enough, however, to prove that a cell in an adjacent grid had to be a certain number, by process of elimination. Sometimes you have to proceed in an indirect fashion.

* That's "puzzle" (or, literally, "head breaker") in Spanish, for you folks in Rio Linda.