MegaSudoku description

MegaSudoku is more difficult and interesting game then ordinary Sudoku. In fact the puzzle contains two, three or even thirteen common sudoku (9x9) connected with each other in one big puzzle. The solution become appreciably more difficult than the solution of sudoku that contains 81 cells.
The ordinary sudoku is number puzzle. The objective is to fill a 9×9 grid with digits so that each column, each row, and each of the nine 3×3 subgrids that compose the grid contains all of the digits from 1 to 9.