Tough Sudoku

Brock,
At 25 filled:
If a1 = 3 or 6, I get e8 = 6 (1 step), but a1 could also be 4 in my setup. If a1 = 4, I needed 4 steps to show row 1 has only 3 numbers for 4 squares.

After eliminating a1 = 4, then e8 = 6 which if I were GB or Ohio Steve would be easy fill to 81 - however I still needed a few eliminations to get there - not totally easy for me. (maybe EF to 81 stands for eliminate and fill)

kaz
In today's puzzle, at 25 filled, I look at the cells d7 = 258, e7 = 458, f7 = 42. For the purposes of the proof, I could care less exactly what each of those three cells contain, only that the union of their contents is 2548 - 4 possibilities in 3 cells. (n being 3). Clearly, then, amongst the many, many non-native weak links this sets contains, is the weak link b7=5 -- c7=4 and b7=5 -- c7=8. By this, I mean nothing more than that both b7=5 and c7=4 or 8 cannot happen at the same time. H

Ok - I mean amongst the many, many non-native weak links that the set implies...are the ones i used in the proof. Hopefully this clears things up.

Basically, I argue that anything that forbids any two (or more)of the possiblities of 2,5,4,8 from the three cells, d7,f7,e7 is forbidden. Then I just pick which of those forbidden occurences forwards whatever proof I choose to use.

forgot to restart the timer
but had a guess anyway
wish it would stop signing we out
havea great day/night one and all

BTW - the penalty for such a step is 3 sets and depth 3 added to whatever other sets and depth are needed in the rest of the proof step.

Congratulations to Fi on a beautiful photo - hope to get the opportunity to see it in real life one day soon

Correction - not sure what I was thinking...If a1 = 3, f9 = 9 (not e8). I think its easiest to show that f9 = 6 is impossible, but it takes me quite a few steps, so maybe your method is easier, but you still have to eliminate a9 = 4.

16:13

38:20 Now that was tough!

Thanks for the explanation but, my word, it's complicated, don't know if I'd ever be able to put it into practice!

Fi, Nice pic hope there's no crocs

We had an easy time with this one- no set up, just patience and logic, no possibilities and no guessing.

Can anyone please tell me how I can populate all the blank squares with every number from 1-9 as possibilities without having to enter each of them one-by-one?

11:11

10:18, a good time for me. good maEveningn

Hi Christina, it's good to read from you again. Any new painting?

Mine was a bit of a mix between Valy's and Brock's I think. Eliminated the 4 in a9 easily but didn't write it out. I know I used the same x-wing as Valy in the process. Then if a9=3, i9=5 and g8=2,so i8=9. Also If a9=3,b79<>3,so b1=3 -> i1=9. Since i8 and i1 cant both be 9, a9 must be 6. Easy from there. Not game yet to try your terminology, though I can follow it now.

1. Unique placemnts to 25
2. X-wing in 7's R19
3. Hidden triple 375 in b1,b7,b9 and b9,h9,i9
4. If a9 = 3 or 6, then e8 must = 6
5. easy fill to 81

step 4 must be wrong
if a9=3, b7=5, e8=5
am I missing something?

am I posting on today's (Still to be done) or yesterday's puzzle, that I've just completed?

19:30 w/couple of guesses.

July 2, 2007.

SE=7.3

24:02.