0 0 1 0 6 3 0 8 6 1 2 8 1 5 7 2 0 4 2 4 1 2 7 9 3 0 9 3 5 5 3 7 3 4 2 7 4 4 6 4 6 1 5 1 3 5 3 7 5 8 2 6 1 2 6 4 5 6 8 3 7 3 1 7 6 8 8 0 3 8 2 6 8 8 1 This puzzle is from Enjoy Sudoku, created with its highest difficulty level: Maelstrom. It cannot be solved with simple elimination. 8 cells get filled in via elimination, and nothing further is possible. Solution, via Enjoy Sudoku: [ note: 0-based row/column/tile ] "Think about block 3". Only row 4 can be contain 8. Thus, eliminate 8 from other tiles' row 4. Thus, tile 5 has a single possible 8 at cell 7,5. [ solve a couple cells ] "Think about block 0". Only column 1 can contain 7. Thus, eliminate 7 from other tile's column 1. "Consider row 1". "Naked Triple". Columns 0 6 8 can only contain 2, 4, or 5. Eliminate these from other cells in the row. "Consider block 1". "Locked Candidates (pointing)". Only row 0 can contain 4. "Look at row 7". "Naked Triple" in columns 1, 2, 8. "Ponder block 3". "Locked Candidates (pointing)". Only column 2 can contain 4. "Hunt for an XYZ-Wing". Pivot at 7,5 with pincers at 2,5 and 7,4. ... One must be 2. Therefore, we can remove 2 from the cells which are neighbors of these three. "Coloring will help"