Sudoku for advanced problem solvers
At expert level, patience matters more than speed. Candidate positions can be linked across multiple units, making a safe elimination depend on several intermediate deductions.
The most reliable approach is to rule out candidates systematically and follow the consequences of every deduction. Aim for a fully reasoned solution rather than guessing.
Refine advanced techniques
Start with pairs and X-Wing, then move on to longer chains and other advanced techniques. Treat every elimination as a small mathematical proof.