Fourth level Sudoku

This is the 5th puzzle session at fourth level of hardness of very hard category. This is a very hard puzzle with multiple bottlenecks to overcome right from the start. Valid DS evaluation for empty cells needs to be done early but in selected cells and limited to 3 digit long DSs. Cross-scan of row, column and 9 cell square, Digit subset analysis and advanced use of Cycles provide the main breakthroughs. Solution of each step with strategies and techniques adopted are explained fully ...

This is the 3rd puzzle session at fourth level of hardness that is placed in very hard category. This is found to be really a very hard puzzle with multiple bottlenecks to overcome right from the start. Valid Digit subset evaluation to a large extent needed to be done very early that indicates the hardness of the puzzle. Digit subset analysis, Cycles and digit lockdown techniques are the primary techniques and resources used for overcoming the bottlenecks. A new structure of chained single digit locks is discovered and converted to a new technique first time. Solution of each step with strategies and techniques adopted explained fully ...