From Sudopedia, the free Sudoku reference guide
Samurai
From Sudopedia
Samurai or Gattai-5 is one of the Sudoku Variations with overlapping constituent Sudoku grids.
The puzzle has 5 grids, with the center grid overlapping exactly one corner box with each of the remaining grids.
Puzzle designers often leave the overlapping boxes without givens, because these would cause too many eliminations, making the puzzle too easy. In a good Samurai, the constituent puzzles cannot be solved without the information provided by the overlapping regions, but the puzzle as a whole has a single solution.
