Comfortable Sudoku'

Sudoku is a logic-based, number-placement puzzle. The objective is to fill empty grid with digits so that each column, each row, and each of the nine 3×3 block that compose the grid contains all of the digits from 1 to 9. Comfortable Sudoku features: Press and hold a grid, you can enter a number directly. 15 different levels of difficulty. Three input modes. Undo / Redo.