Extreme difficulty (maybe unsolvable?) killer sudoku : r/sudoku

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Sudoku solving algorithms - Wikipedia

Help! I found this killer cage that seems impossible. It has no givens and follows standard killer cage rules. I haven't even put a single pencil mark. : r/sudoku

A-Z Sudoku, PDF, Vertex (Graph Theory)

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Sudoku solving algorithms - Wikipedia

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Hard killer sudoku - Solve free puzzles online

How hard is this Killer Sudoku? : r/sudoku

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r/Sudoku: a place to learn it and enjoy it

Killer Sudoku help! I can't get the online answer for this but have been dying to solve it but keep going wrong. If anyone is happy to help please let me know!

really hard sudoku - Caravel Forum