Tridoku Puzzles 400 Tridoku Sudoku Puzzles: Hard Triangular Sudoku Puzzles, Book 12, (Paperback)

The puzzle consists of nine large triangles; the numbers 1 through 9 must be placed into the triangular cells of each large triangle. Also, the numbers 1 through 9 must be placed in the three legs of the inner shaded triangle and in the three legs of the outer shaded triangle. No two neighboring cells may contain the same number.