Calcu-doku has taken the puzzle world by storm, providing solvers with many happy hours of logical thinking and simple mathematics. Now, world sudoku champ Thomas Snyder takes it to the next level. He ups the ante by incorporating unique themes into the mix: so your starting numbers might be in the shape of a smiley face, or the secret to solving might revolve around the number 5. Snyder has pulled out all the stops-and created a compelling, captivating, and creative variation on Calcu-doku.