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A Sudoku Challenge: The Carriage House Puzzle

Laura Taalman, of James Madison University, finds sudoku puzzles endlessly fascinating. She has created a wide variety of entertaining variants, and she described many of them during her presentation at last week's MAA Carriage House Conference Center opening celebration.

In "snowflake" sudoku, for example, the numbers from 1 to 9 are filled in so that no number is repeated in any row, column, block, or various diagonals. In color variants, the usual sudoku rules apply, but no number can appear more than once with any color. Some of these variants can be seen at her "Brainfreeze Puzzles" Web site at, with a book, Color Sudoku, on the way.

In honor of the Carriage House opening, Taalman created a challenging puzzle (below) in which each row, each column, and each jigsaw region must contain each of the letters  in "CARRIAGE HOUSE." Note that this means each row, column, and region will contain the letters "A," "R," and "E," twice.


"It's very hard," Taalman warns.

There are lots of open mathematical problems associated with sudoku, many of which lend themselves to undergraduate research projects, Taalman says. Although these extremely popular puzzles typically don't involve even arithmetic, they're wonderful exercises in logic—and lend themselves to illuminating excursions into such mathematical topics as combinatorics, Latin squares, polyominoes, computer algorithms, chess problems, graph colorings, and permutation group theory.

To obtain or print a PDF copy of the puzzle, use the following link: Carriage House Sudoku (PDF version).

News Date: 
Tuesday, April 24, 2007