4) Gattai-5 Number 2.
As you can see, this puzzle consists of 5 overlapping 9-by-9 grids. Each one must be filled in according to standard Sudoku rules. However, you will find that none of the grids can be filled in alone: instead, you must solve as much as you can in any 9-by-9 grid, taking the grids in turn. Partial solution of one grid will help with that of overlapping grids either by actually solving for one or more of the overlapping entries, or by reducing the range of candidates available for particular overlapping squares.