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Saturday 24-Feb-2018

... by: Paolo Calaresu

Basics R2C7=5 and R9C23≠4
After Basics
7R3C2=>contradiction (R5C4=)=>-7R3C2
7R3C6=>contradiction (nessun 9 in riga 3)=>-7R3C6
2R7C3=>contradiction (R9C8=)=>-2R7C3
It is formed the Back-door R6C1=2
To demonstrate the uniqueness of the solution:
2R5C1=>contradiction (R1C3=)=>-2R5C1
2R3C1+4R6C9=>contradiction (nessun 3 in riga 5)
2R3C1+7R6C9=>contradiction (R7C8=)
2R3C1+8R6C9=>contradiction (R7C6=)=>-2R3C1

2R1C1+2R9C2=>contradiction (R1C2=)
2R1C1+3R9C2=>contradiction (R8C2=)
2R1C1+5R9C2=>contradiction (R7C5=)=>-2R1C1=>solution.


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