2005/09/12 tough puzzle from sudoku.com.au

Initial position :

1) Easy eliminations : c7=8%col, g3=4%col, c5=2%col, c3=9%cell, c1=7%col, g5=3%cell, c2=4%cell, d1=4%block, d1=4%row, g7=2%cell, lead to (for better reading, only remaining possibilities in still empty cells are written).

2) Look at 9 in Be2 : 9 is in R2, so no other 9's in R2.

16 are the only choices in a1 and in b1, so you can eliminate all 1s and 6s except these as possibilities in Row1 and Blockb2.
Perform the same with the only choices : 89 in g8 and g9, then 36 in h9 and i9, then 28 in e1 and e9. We're at

3) Look at 5 in Bh5. Wether it is in R4, in which e4=1%cell, or it is in h5 in which h8=1%cell : e8=3%cell. Follow now easy eliminations (d6=3%block, e6=6%cell, b5=6%block, a1=6%block, b1=1%block, a4=1%block, e2=1%col, e4=5%col, h5=5%block, i7=5%block, h8=1%block, i3=1%block) up to :

4) Look at Be8. Now 28 are in d8e9 no matter the order, eliminate others 2 and 8 from Be8. Follow then easy eliminations (f8=4, f9=7%cell, d5=7%row, f5=1%block, d7=1%block, f7=6%block) up to :

5) Now look at e1. Wether e1=2, in which d8=2%block, a8=5%cell, or e1=8, in which f3=5%cell,b2=5%row : b8=9%cell. Now easy eliminations lead to unique solution.

(Details if needed : g9=9%block, g8=8%block, e9=8%block, a8=5%block, b2=5%block, f3=5%block, d3=8%block, h1=8%block, i1=9%block, d2=6%block, f2=9%block, d4=9%block, h6=9%block, h4=7%block, h3=6%block, i9=6%block, h9=3%block, i2=3%block, a3=3%block, b7=3%block, a7=7%block, b6=7%block, b4=8%block, f6=8%block, a6=4%block, b9=4%block, i4=4%block, d8=2%block, a9=2%block, i6=2%block, f4=2%block, h2=2%block, e1=2%block).

Note : Equivalent puzzles are : 09/26, 09/27, 09/29, 10/02.