The New Sudoku Players' Forum

[tonyburnaby]

I am stuck, could be done by guessing and trial/error, but I am wondering whether I can solve this puzzle just by logical thinking without guessing? thanks a lot.

Here is the puzzle:

[JC Van Hay]

Analysis of the puzzle :

Implications of the 8 cells containing the digits 57 (using Red Green Transport)!

If r1c4=5 => r4c2=5, r8c2=9, r1c2=8=r6c1, r5c1=1
While
If r1c4=7 => r8c1=9; r5c1=1

Furthermore, r5c1=1 => r1c4=7

Finally : r6c1=1 => r5c1=9 & r1c1=8, r1c2=9; no 9 in R8!

Interpretation :

#1. Chain[4] : 8r6c1=8r1c1-(8=9)r1c2-9r8c2=9r8c1-(9=1)r5c1 :=> -1r6c1; 16 singles

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The puzzle is then solved using :

#2. BUG+1 : +5r6c2; singles to the end
Or
#2. Chain[3] : XY Wing : (8=5)r6c1-(5=98)r14c2 :=> -8r1c1.r6c2; singles to the end

[tonyburnaby]

a bit overwhelming, but I finally got your explanation, thanks so much!