2005/10/11 tough puzzle from sudoku.com.au

This one is equivalent to 05/09/28. Proof :

1) Take 05/09/28 grid.

2) Now move rows 123456789 (1=bottom!) on new positions 132654879

3) Now move columns abcdefghi(a=left!) on new positions bcafedigh. Do you begin to feel like déjà vu?

4) All that's left now is to rename last grid's values 123456789 on 395826417 and you get exactly 05/10/11's puzzle.

Now applying the same "dictionary" (changing rows, columns, values) to proof of 05/09/28 you will mechanically get a proof of today's. Try it ! Or see the method explained step by step on 10/08 example.

See more illustrated examples of equivalence between puzzles : 09/26,09/29, 10/02, 10/03, 10/04.
See equivalent puzzles : 17,21,28 sept, 4,6,11 oct.

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In case that you be lazy enough not to find it by yourself, here is the proof automatically derived from 09/28's proof.

Initial position :

[Maple Plot]

1) Easy eliminations : g3=1%block, d7=6%block, g9=6%block, f9=8%row, e9=5%row, lead to (for better reading, only remaining possibilities in still empty cells are written) :

[Maple Plot]

2) a) 3 in Bh2 is in R1, and so forbids {c1=3, a1=3, e1=3},

b) samely 9 in Bh2 is in Ch, and so forbids {h6=9, h5=9, h7=9, h8=9},

c) samely 5 in Be5 is in R5, and so forbids {c5=5, b5=5, h5=5, g5=5}, hence 56 in Cb are in b3b4 so no other value possible in b3b4.

d) 34 are in f78 so no other 17 in Be8 or in Cd.

Now come some more simple eliminations f2=2%cell, e3=3%block, b2=8%col, d1=8%block, c1=5%row, b3=6%cell, b4=5%cell, c4=6%block, h1=6%block, c3=2%block, e7=9%col, d8=1%block, e6=1%block, so here we are with 39 filled cells :

[Maple Plot]

3) 74 are in a1a3 and nowhere else in Ca and Bb2. 49 are in h23 and nowhere else in Ch and Bh2, from which follow new simple eliminations : h5=7%cell, e4=7%block, e1=4%cell, d2=9%cell, h2=4%cell, d3=5%cell, f3=7%cell, a3=4%cell, h3=9%cell, a1=7%cell, c6=7%block, d5=4%block, f5=5%block, h8=5%cell, g6=5%block, and here we are with 54 filled cells :

[Maple Plot]

4) Look at 9 in column Cc : whether c9=9 (in which i9=4%row) or c5=9, g8=9 (%cell or %col). (Heptagon).

From here simple eliminations end to unique solution. (Details if needed : g8=9%cell, i6=9%block, c5=9%block, a9=9%block, h6=2%block, g4=8%block, a4=3%cell, a2=1%cell, c2=3%cell, h7=8%block, a6=8%block, i4=4%block, g7=4%block, f8=4%block, c9=4%block, b5=1%block, c7=1%block, i9=1%block, g5=3%block, g1=2%cell, i1=3%cell, i7=2%block, i8=7%block, b7=7%block, b9=2%block, f7=3%cell, b8=3%block).

[Maple Plot]

That's all for today, folks...

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Dictionary from 09/28 to 10/11 :

[Maple Plot]