Unlike many sudoku, where a third of the squares are filled in, each of these puzzles has only 18 givens (completed squares). That means fans enjoy more of a challenge. All the puzzles are expertly crafted to satisfy both casual solvers on a break and sudoku die-hards relaxing on a Sunday afternoon. About the Author: PHILIP RILEYis a software developer and the author of numerous computer programs that analyze variants of sudoku puzzles.LAURA TAALMANis a professor of mathematics at James Madison University,Harrisonburg, Virginia. Key Selling Points: - No other book of puzzles out there like this, so solvers are in for a unique treat