dailysudoku.com Forum Index dailysudoku.com
Discussion of Daily Sudoku puzzles
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

An Extended Form of Medusa Coloring
Goto page Previous  1, 2
 
Post new topic   Reply to topic    dailysudoku.com Forum Index -> Solving techniques, and terminology
View previous topic :: View next topic  
Author Message
Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sat Feb 02, 2008 12:38 am    Post subject: Reply with quote
I only went two days this time. Can an inference be made based on an assumption of true in two or more cells? Consider these two cells in a line:

23g 2g34

Can we say that if 2g3g are both true, then the 4 can be inferred, thus creating a wrap? Seems too easy.

Or this:

38g 35g 158

Can we infer the 1 assuming that the 5g8g are both true?
Back to top
View user's profile Send private message
Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA
PostPosted: Sat Feb 02, 2008 7:02 am    Post subject: Reply with quote
Marty R. wrote:
Can an inference be made based on an assumption of true in two or more cells?

Yes, but...

In your first example, I don't see that there is any inference about the <4> in those two cells. We only know that the <4> is false if G is true (since in that case the cell must be <2>). But, that isn't very helpful. I certainly can't see a "wrap."

However, if that <4> were strongly linked to another <4> that already shared a cell with a "g" value, then you would have a wrap (since G would eliminate all <4>s in that house).

In the second example, we can infer that the <1> is "g", but not that it is true. In other words, if G is true, then the third cell must be <1>, hence, it can be colored "g".

I hope that is clear.
Back to top
View user's profile Send private message Visit poster's website
Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Sat Feb 02, 2008 4:16 pm    Post subject: Reply with quote
A,

Thanks, I hope for the last time.

I wasn't thinking very clearly when I presented my first example. How can you infer a cell is "x" if you assume it's "y'"? Embarassed
Back to top
View user's profile Send private message
Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Thu Feb 21, 2008 4:29 pm    Post subject: Reply with quote
Consider the following partial grid with made-up numbers just to illustrate the point:

Code:
+-------+-------+-----------+
| . . . | . . . | 49g .   . |
| . . . | . . . | 139 .   . |
| . . . | . . . | 13  .   . |
+-------+-------+-----------+
| . . . | . . . | 17  .   . |
| . . . | . . . | .   69g . |
| . . . | . . . | .   .   . |
+-------+-------+-----------+
| . . . | . . . | .   .   . |
| . . . | . . . | .   .   . |
| . . . | . . . | .   .   . |
+-------+-------+-----------+

The 9g in box 6 has inferred the 9g in box 3. The latter 9g infers a naked 13 pair just below it. Is this a legitimate trap whereby r4c7 can be solved for 7? I'm used to my traps coming from little r's and g's.

Or is all we can do is mark the 7 with a "g"?

(First question in 20 days). Very Happy
Back to top
View user's profile Send private message
Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA
PostPosted: Fri Feb 22, 2008 12:02 am    Post subject: Reply with quote
Marty wrote:
Is this a legitimate trap whereby r4c7 can be solved for 7? ... Or is all we can do is mark the 7 with a "g"?

All you can do is mark the 7 with a "g". The <1> can only be removed if it can "see" a red <1> somewhere.

[Edit to remove unnecessary comment.]
Back to top
View user's profile Send private message Visit poster's website
Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Fri Feb 22, 2008 1:19 am    Post subject: Reply with quote
As always, thanks.
Back to top
View user's profile Send private message
Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Mon Mar 31, 2008 12:35 am    Post subject: Reply with quote
Code:
+-------+-------+---------+
| . . . | . . . | . .   . |
| . . . | . . . | . 4a8 . |
| . . . | . . . | . .   . |
+-------+-------+---------+
| . . . | . . . | . .   . |
| . . . | . . . | . 36b . |
| . . . | . . . | . .   . |
+-------+-------+---------+
| . . . | . . . | . .   . |
| . . . | . . . | . .   . |
| . . . | . . . | . 469 . |
+-------+-------+---------+

The actual values shown are just for illustration. If I infer from the 4a, then r9c8 = 69. If I infer from the 6b, then r9c8 = 49. The 9 is there based on inferences from both a and b, so I placed it. Valid or did I just get lucky this one time?
Back to top
View user's profile Send private message
Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA
PostPosted: Tue Apr 01, 2008 8:37 pm    Post subject: Reply with quote
Marty wrote:
Valid or did I just get lucky this one time?

I believe that was luck. I don't see it as a valid placement. All you know is that r9c8 is either {69} or it is {49}. <4> and <6> are still possibilities.
Back to top
View user's profile Send private message Visit poster's website
Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Tue Apr 01, 2008 9:22 pm    Post subject: Reply with quote
As always, thanks. I guess I'll avoid that type of thing in the future. But I do understand what you're saying.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    dailysudoku.com Forum Index -> Solving techniques, and terminology All times are GMT
Goto page Previous  1, 2
Page 2 of 2

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group