... by: Vinay

Solved 'Unsolvable' #154

... by: MLS

Correction:B5=3 leads to solution

... by: MLS

B2=3 leads to solution

... by: qoheleth

Andrew, some time ago I inquired about a dump of techniques used to solve an ordinary Sudoku. You replied that you were working on an eBook along those lines. I asked to be remembered if it were ever published. Some time has no elapsed and I've been wondering where you are in the project.

... by: rkeech

I usually fail in my attempts to solve the weekly unsolvable puzzles, as I am at best a mediocre solver of Sudoku puzzles, but each one teaches me something new. For #154, all the pieces somehow fell into place, and I finished in 4 minutes and 15 seconds! It usually takes me Ionger to do the very easy ones. I know that I am getting better over time, but this time, everything just fell into place!

... by: Glenn D

Unsolvable Puzzle #154. I have solved this puzzle using the following technique. Whether this is guessing, I will leave it up to you to decide. In every Sudoku we solve we must start with a candidate in a cell to see if we can make a deletion/deletions be it a Digit Forcing Chain, X-Y Chain, Nishio Chain, or X-chain using our selected candidate. We are not sure our selection will “work” until we try. The same here is also true. If you put Unsolvable #154 in the Scanraid Solver, keep making deletions until Scanraid tells you the puzzle is unsolvable.
Now arbitrarily select 3(r8c5), 1(r2c5), 1(R8C3). You now have in row 8, (3) cells with 7,8 in them so we now that can’t be. We conclude that the 3 we chose as a start candidate, is not valid nor are any deletions we have made using it are valid. But we do know that the 1 in (r8c5 is valid. Now Scanraid will solve this puzzle albeit with a grade rating of over 730. I always start with a bivalve so I know if my start number is not valid, the remaining candidate is valid. Sometimes you have to make a lot of deletions before you can confirm the validity of your selection.
This one was pretty easy but most are more involved but if you work with them, you will be rewarded. You can solve a lot of puzzles this way. Valid way to go?????

... by: dsf

fds

... by: newby

9A1, 5J9, 5B3, 5F2, 2F5, 2E1, 9G5, 4D5, 9J7
(4E2,4F3)7E8>contradiction therefore 1E8
(4E2,4F3)3H5>contradiction therefore1H5, 3B5, 1B7, 9F6
(4E2,4F3)8B1>contradiction therefore 7B1, 8B9
(2G3,2J3)4E2>contradiction therefore 4F3, 4E9, 4A7, 8F7
2J3>contradiction therefore 2G3 solves

... by: Joss Rogan

@ JPF Naperville - Time to solve---15 minutes ? You must be like me, I fall asleep half way through too. Your description is precisely correct for easily solving this excellent puzzle. What's all this swordfish and bi-location stuff mentioned by the others?

... by: JPF NAPERVILLE

Thanks for the early Xmas present. #154(the first new 'unsolveable' since Oct.4-10) was readily solved using only steps 1-6 to yield 10
fill-ins, and then solving the quad in row H via testing a 3 in cell H7.
No need for any steps from 7-35 just basic candidate search logic and then combination analysis . Time to solve---15 minutes!!

... by: ray

#1. Use basic strategies to get working board and apply bi-location tool.
#2. Choose cell J9{3679} - bi-location cell for 6, tri-location cell for 3 and 6.
Forcing J9 = 3 or 6 gives inconclusion, J9 = 7 gives the solution.Using
this solution,other bi-location 1-cell solutions found are: J3 = 6; other
1-cell solutions are:H7 = 3; some 2-cell solutions are: DF7 = (7,8),
G23 = (4,2), D1H5 = (6,1). Note: only basic strategies were used.

... by: JC Van Hay

#1. 10 Singles; Swordfish(3C159)-3H3.B7; XWing(6C19)-6D7; Jellyfish(8R2468)-8ACGJ1379

#2. F7=4 -> G7=6, A9=4, GJ3=24, XWing(3HJ1,3H7J9)-(3=1)H5, B7=1=J2, J1=6, H1=3=J9, XWing(78C19)-(78)D7; D7={} :=> A7=4

#3. 3H7=HP(23-6)CG7=6J9-...-Kite(6JD1,6E29)=HT(631)E468-1D7=*[1H5=1B5-1B7=*(1-2)C7=HP(23)GH7] :=> -3J9.H5; 9 Singles

#4. (78=3)H13-3H7=(3-6)G7=6G3-(6=378)J1.H13 :=> -7GJ23,-8BJ2.H7; Singles to the end.