The New Sudoku Players' Forum

by **ronk** » Fri Jul 27, 2007 8:10 pm

denis_berthier wrote:column C7 : hxy5-rn-chain on rn-cells R1N3*, R1N9, R4N9, R4N4 and R7N4* with columns C7, C3, C1, C3 and C1
==> C7 eliminated from the rn-candidates for R1N4
i.e. 4 eliminated from the candidates for R1C7

Code: Select all: .8.2.1...14.385.92.2.9.4.18.3.758261261493.8.8..612934.98137.2....8291.3312546879 rc-spc| c1 c2 c3 | c4 c5 c6 | c7 c8 c9 ------+-------------------+-------------------+------------------- r1 | B5679 8 A35679 | 2 67 1 | 3567-4 45 567 r2 | 1 4 67 | 3 8 5 | 67 9 2 r3 | 567 2 3567 | 9 67 4 | 3567 1 8 ------+-------------------+-------------------+------------------- r4 |CE49 3 D49 | 7 5 8 | 2 6 1 r5 | 2 6 1 | 4 9 3 | 57 8 57 r6 | 8 57 57 | 6 1 2 | 9 3 4 ------+-------------------+-------------------+------------------- r7 | F456 9 8 | 1 3 7 |G456 2 56 r8 | 4567 57 4567 | 8 2 9 | 1 45 3 r9 | 3 1 2 | 5 4 6 | 8 7 9 rn-spc| n1 n2 n3 | n4 n5 n6 | n7 n8 n9 ------+-------------------+-------------------+--------------- r1 | 6 4 a37 | 8-7 13789 13579 | 13579 2 b13 r2 | 1 9 4 | 2 6 37 | 37 5 8 r3 | 8 2 37 | 6 137 1357 | 1357 9 4 ------+-------------------+-------------------+------------------- r4 | 9 7 2 |d13 5 8 | 4 6 c13 r5 | 3 1 6 | 4 79 2 | 79 8 5 r6 | 5 6 8 | 9 23 4 | 23 1 7 ------+-------------------+-------------------+------------------- r7 | 4 8 5 |e17 179 179 | 6 3 2 r8 | 7 5 9 | 138 1238 13 | 123 4 6 r9 | 2 3 1 | 5 4 6 | 8 7 9 a b c d e r1n4-7-r1n3-3-r1n9-1-r4n9-3-r4n4-1-r7n4-7-r1n4, implies r1n4<>c7 i.e. r1c7<>4

It should be no surprise that bivalues in rn-space are bilocation values in standard rc-space. Using all the cells in the hxy5 chain, but in rc-space ...

Code: Select all: A B C(E) D E(C) F G r1c7=3=r1c4=9=r1c1-9-r4c1=9=r4c3=4=r4c1-4-r7c1=4=r7c7-4-r1c7, implies r1c7<>4

That r4c1 appears twice is a bit weird, but it's logically correct, and it means the deduction does not depend on the bivalues in r4c1 and r4c3.

Hmm, I wonder how many solvers would not find this (if r4c1 and r4c3 were not bivalues) because overlaps are not allowed.

[edit: formatted rn-pencilmarks]

by **re'born** » Fri Jul 27, 2007 9:22 pm

denis_berthier wrote:
re'born wrote:
denis_berthier wrote:.8.2.1…
14.385.92
.2.9.4.18
.3.758261
261493.8.
8..612934
.98137.2.
…8291.3
312546879

In this puzzle, you've inadvertantly replaced "."'s with ellipses in row 1 and row 8. This makes it rather troublesome to copy into solvers.

re'born, thanks for signaling it. In my navigator, I don't see that. Have you corrected it in the above?

I didn't correct it. It has happened to me before, usually if my text editor has a built in auto-correct, since these usually turn 3 consecutive periods into ellipses. This explanation at least fits the facts (modulo me not knowing what text editor you used to originally write down the grid).

by **re'born** » Fri Jul 27, 2007 9:46 pm

Inspired by ronk's analysis, I took a peek at the rn-space and found a very pretty almost xy-ring (would this translate in the rc-space to an halmost xy-ring?

)

Code: Select all: rn-spc| n1 n2 n3 | n4 n5 n6 | n7 n8 n9 ------+-------------------+-------------------+--------------- r1 | 6 4 37 | 78 13789 1579-3 |1579-3 2 13 r2 | 1 9 4 | 2 6 37b | 37a 5 8 r3 | 8 2 37 | 6 137 157-3 | 157-3 9 4 r4 | 9 7 2 | 13 5 8 | 4 6 13 r5 | 3 1 6 | 4 79 2 | 79 8 5 r6 | 5 6 8 | 9 23 4 | 23e 1 7 r7 | 4 8 5 | 17 179 179 | 6 3 2 r8 | 7 5 9 | 38-1 238-1 13c |12(3)d 4 6 r9 | 2 3 1 | 5 4 6 | 8 7 9

The almost xy-ring (labelled a-e above) eliminates from rn-space r13n67<>3, r8n45<>1, which in rc-space corresponds to
r13c3<>6,7 and r8c1<>4,5. This doesn't even come close to solving the puzzle, but it was the first xy-ring (or almost xy-ring) I've seen in rn-space.

Question: What sort of pattern makes these exclusions in rc-space?

[Edit: Changed xy-cycle to xy-ring (thanks ronk for pointing that out)]
[Edit2: Fixed my notation (thanks Denis, old habits will die hard)]

Website · by **denis_berthier** » Sat Jul 28, 2007 3:48 am

re'born wrote:The almost xy-ring (labelled a-e above) eliminates from rn-space r13c67<>3, r8c45<>1

Of course, you mean: r13n67<>3, r8n45<>1

re'born wrote:Question: What sort of pattern makes these exclusions in rc-space?

The advantage of rn- and cn- spaces is that they make some complex patterns of rc-space appear as simple ones in rn-space.

Ronk's analysis of my example in a previous post is interesting: the simple hxy-chain on 5 rn-cells:
hxy5-rn-chain on rn-cells R1N3*, R1N9, R4N9, R4N4 and R7N4* with columns C7, C3, C1, C3 and C1
appears in rc-space as a discontinuous AIC on 7 cells (not counting the target R1C7)
r1c7=3=r1c4=9=r1c1-9-r4c1=9=r4c3=4=r4c1-4-r7c1=4=r7c7-4-r1c7

As you notice, "that r4c1 appears twice is a bit weird, but it's logically correct" and I think few people will find it because such internal loops are generally not looked for.

All hxy-chains are AICs (simply because a bivalue in rn- or cn- space corresponds to a bilocation in rc-space), but they often look much simpler (and are thus much simpler to find).
Notice that, conversely, not all AICs will appear as hxy-chains.

Nevertheless, for more complex chains in rn- or cn- space, there may be no known corresponding pattern in rc-space. This is in general the case for hxyt and hxyzt- chains.
In the case of your ring, I have no answer.

When I discovered rn- and cn- spaces, I initially did the same as you: I wondered what these patterns correspond to in "normal" space. Now, I know the answer is generally complex and I just take them as they are. Their have the same right to independent existence as any pattern in rc-space.

by **ronk** » Sat Jul 28, 2007 10:58 am

denis_berthier wrote:r1c7=3=r1c4=9=r1c1-9-r4c1=9=r4c3=4=r4c1-4-r7c1=4=r7c7-4-r1c7

As you notice, "that r4c1 appears twice is a bit weird, but it's logically correct" and I think few people will find it because such internal loops are generally not looked for.

As stated earlier, that nice loop was forced to use all the cells of the hxy5 chain which means it was contrived. As there is no need to look for an "internal loop", it is not what someone would normally find. The bivalue/bilocation plot solver would most likely instead find ...

r1c7=3=r1c4=9=r1c1-9-r4c1-4-r7c1=4=r7c7-4-r1c7

... which, like the hxy5 chain, uses five cells.

by **re'born** » Sat Jul 28, 2007 5:11 pm

ronk wrote:
denis_berthier wrote:r1c7=3=r1c4=9=r1c1-9-r4c1=9=r4c3=4=r4c1-4-r7c1=4=r7c7-4-r1c7

As you notice, "that r4c1 appears twice is a bit weird, but it's logically correct" and I think few people will find it because such internal loops are generally not looked for.

As stated earlier, that nice loop was forced to use all the cells of the hxy5 chain which means it was contrived. As there is no need to look for an "internal loop", it is not what someone would normally find. The bivalue/bilocation plot solver would most likely instead find ...

r1c7=3=r1c4=9=r1c1-9-r4c1-4-r7c1=4=r7c7-4-r1c7

... which, like the hxy5 chain, uses five cells.

I haven't checked it, but I think the above loop will correspond to an hxy-chain in cn-space. In my limited experience, I have seen that if an hxy-chain in rn-space (resp. cn-space) corresponds to a chain with internal loops in rc-space, then there is a corresponding chain in cn-space (resp. rn-space) that makes the same exclusions but doesn't have the internal loop.

Website · by **denis_berthier** » Sun Jul 29, 2007 8:37 am

Raining cats and dogs outside ==> time (and weather) for more complex examples.

Consider the following (very hard) puzzle:
600700400
904060000
758000600
491000208
800009314
200841960
340007000
107980543
589000726

After a few elementary eliminations:

Code: Select all: row R4 interaction with block B5 ==> 6 eliminated from the candidates for R5C4 row R9 interaction with block B8 ==> 1 eliminated from the candidates for R7C5 ==> 1 eliminated from the candidates for R7C4 xy-wing on cells R5C3*, R7C3 and R7C5* with numbers 5, 6 and 2 ==> 5 eliminated from the candidates for R5C5 xy-wing on cells R5C4*, R5C3 and R7C3* with numbers 2, 5 and 6 ==> 2 eliminated from the candidates for R7C4

you need a succession of moderately complex chains of various types (xy, hxy, hxyt, hyyzt, c), illustrating how you can juggle with rc- and rn- spaces;
(for the definitions of xyt and xyzt, see the other thread;
c-chains are the simplest AICs
a * on a cell indicates that any target cell of the chain must be connected to it, in the space of this chain: rc, rn or cn);
these steps are a good way to get used with all these chains:

Code: Select all: hxy4-rn-chain on rn-cells R5N5*, R5N6, R8N6 and R4N6* with columns C4, C3, C2 and C6 ==> C4 eliminated from the rn-candidates for R4N5 i.e. 5 eliminated from the candidates for R4C4 c4-chain row-bl-col on cells R8C6-R8C2-R7C3-R1C3 ==> 2 eliminated from the candidates for R1C6 xy5-chain on cells R5C5*, R5C2, R5C3, R6C3 and R1C3* with numbers 2, 7, 6, 5 and 3 ==> 2 eliminated from the candidates for R1C5 xyt5-chain on cells R7C5*, R7C4, R4C4, R4C5 and R5C5* with numbers 2, 5, 6, 3 and 7 ==> 2 eliminated from the candidates for R3C5 hxyzt5-rn-chain-type-3 on rn-cells R3N4*, R9N4, R9N1, R3N1* and R3N2* with columns C4, C6, C4, C5 and C9 ==> C4 eliminated from the rn-candidates for R3N3 i.e. 3 eliminated from the candidates for R3C4 xy6-chain on cells R5C4*, R5C5, R5C2, R8C2, R8C6 and R7C4* with numbers 5, 2, 7, 6, 2 and 6 ==> 5 eliminated from the candidates for R2C4 xyzt7-chain-type-1 on cells R1C3*, R1C2*, R2C2, R6C2, R6C9, R1C9 and R3C8* with numbers 3, 2, 1, 3, 7, 5 and 9 ==> 3 eliminated from the candidates for R1C8

then comes a monster hxyt-rn-chain of length 10, which makes two decisive eliminations:

Code: Select all: hxyt10-rn-chain on rn-cells R2N7*, R6N7, R5N7, R5N2, R5N5, R5N6, R8N6, R8N2, R2N2 and R2N5* with columns C8, C9, C2, C5, C4, C3, C2, C6, C2 and C6 ==> C8 eliminated from the rn-candidates for R2N8 i.e. 8 eliminated from the candidates for R2C8 ==> C8 eliminated from the rn-candidates for R2N3 i.e. 3 eliminated from the candidates for R2C8

If you have reached this point, you'll easily find how to finsih.

Of course, such a exceptionally long chain is hard to find. But this is an extreme example. Usually, chains will be much shorter.

by **daj95376** » Sun Jul 29, 2007 4:21 pm

denis_berthier wrote:Raining cats and dogs outside ==> time (and weather) for more complex examples.

Consider the following (very hard) puzzle:
600700400
904060000
758000600
491000208
800009314
200841960
340007000
107980543
589000726

After a few elementary eliminations:

Set any one of 14 bi-value cells to the wrong value:

Code: Select all: [r1c3]=3,[r4c8]=5,[r5c2]=7,[r5c3]=6,[r5c4]=5,[r5c5]=2,[r6c2]=3, [r6c3]=5,[r6c9]=7,[r7c3]=2,[r7c4]=6,[r7c5]=5,[r8c2]=6,[r8c6]=2 => 16 Naked Singles, [r2c8]=h7, [r2c6]=h3 => [c6]=Invalid

After choosing a correct value in one of these cells, Singles complete the puzzle.

Website · by **denis_berthier** » Sun Jul 29, 2007 4:35 pm

daj95376 wrote:600700400
904060000
758000600
491000208
800009314
200841960
340007000
107980543
589000726

Set any one of 14 bi-value cells to the wrong value:

Code: Select all
[r1c3]=3,[r4c8]=5,[r5c2]=7,[r5c3]=6,[r5c4]=5,[r5c5]=2,[r6c2]=3, [r6c3]=5,[r6c9]=7,[r7c3]=2,[r7c4]=6,[r7c5]=5,[r8c2]=6,[r8c6]=2 => 16 Naked Singles, [r2c8]=h7, [r2c6]=h3 => [c6]=Invalid

After choosing a correct value in one of these cells, Singles complete the puzzle.

Trial and Error is generally not accepted as a valid method.

by **daj95376** » Sun Jul 29, 2007 4:54 pm

Yes, I can see where your solution is easier and more intuitive!

by **re'born** » Fri Aug 24, 2007 10:02 am

Here is a nice example I recently found of an hxy-ring:

Code: Select all: 4 3 .|. 1 .|. . 9 . . 1|. . .|. . . . . .|4 . .|7 3 1 -----+-----+----- . 6 .|5 7 1|3 9 4 1 5 9|3 . 4|2 . 7 7 4 3|2 . .|1 5 . -----+-----+----- 3 2 6|7 4 8|9 1 5 5 . .|. . .|8 . . 9 . .|. 5 2|. 7 3

After removing a couple of locked candidates, we get

Code: Select all: .------------------.------------------.------------------. | 4 3 257 | 68 1 567 | 56 268 9 | | 26 79 1 | 689 2369 35679| 456 2468 268 | | 268 89 258 | 4 269 569 | 7 3 1 | :------------------+------------------+------------------: | 28 6 28 | 5 7 1 | 3 9 4 | | 1 5 9 | 3 68 4 | 2 68 7 | | 7 4 3 | 2 689 69 | 1 5 68 | :------------------+------------------+------------------: | 3 2 6 | 7 4 8 | 9 1 5 | | 5 17 47 | 169 369 369 | 8 246 26 | | 9 18 48 | 16 5 2 | 46 7 3 | '------------------'------------------'------------------'

Switching to RN-space, we get

Code: Select all: n1 n2 n3 n4 n5 n6 n7 n8 n9 ----------------------------------------------------------------------- r1| 5 38 2 1 367 4678 36 48 9 r2| 3 1589 56- 78* 67* 1456789-26* 489 2456- r3| 9 135 8 4 36 156 7 123 256 r4| 6 13 7 9 4 2 5 13 8 r5| 1 7 4 6 2 58 9 58 3 r6| 7 4 3 2 8 569 1 59 56 r7| 8 2 1 5 9 3 4 6 7 r8| 24 89 56 38* 1 45689 23* 7 456 r9| 24 6 9 37 5 47 8 23 1

an xy-ring that implies r2n369<>6 and r2n6<>7. This translates in the original grid to r2c6<>369 and r2c7<>6. After some cleaning up, the puzzle is reduced to

Code: Select all: .---------------.---------------.---------------. | 4 3 257 | 68 1 567 | 56 268 9 | | 26 79 1 | 689 3 57 | 45 2468 268 | | 68 89 58 | 4 2 569 | 7 3 1 | :---------------+---------------+---------------: | 28 6 28 | 5 7 1 | 3 9 4 | | 1 5 9 | 3 68 4 | 2 68 7 | | 7 4 3 | 2 689 69 | 1 5 68 | :---------------+---------------+---------------: | 3 2 6 | 7 4 8 | 9 1 5 | | 5 17 47 | 169 69 3 | 8 246 26 | | 9 18 48 | 16 5 2 | 46 7 3 | '---------------'---------------'---------------'

where the short chain
[r8c4]-1-[r8c2]-7-[r2c2]-9-[r2c4]=9=[r8c4], =>r8c4<>1, solves the puzzle.

Edit: Alternatively, if one looks at CN-space from the start, there is an xy-chain
-2-[c2n7]-8-[c2n1]-9-[c4n1]-8-[c4n9]-2-, =>c2n9<>2 =>r2c2<>9, solving the puzzle.

by **ronk** » Fri Aug 24, 2007 3:22 pm

re'born wrote:Switching to RN-space, we get
Code: Select all
n1 n2 n3 n4 n5 n6 n7 n8 n9 ----------------------------------------------------------------------- r1| 5 38 2 1 367 4678 36 48 9 r2| 3 1589 56- 78* 67* 1456789-26* 489 2456- r3| 9 135 8 4 36 156 7 123 256 r4| 6 13 7 9 4 2 5 13 8 r5| 1 7 4 6 2 58 9 58 3 r6| 7 4 3 2 8 569 1 59 56 r7| 8 2 1 5 9 3 4 6 7 r8| 24 89 56 38* 1 45689 23* 7 456 r9| 24 6 9 37 5 47 8 23 1

an xy-ring that implies r2n369<>6 and r2n6<>7. This translates in the original grid to r2c6<>369 and r2c7<>6.

That hxy5 continuous loop uses the strong inferences of five bivalues. While the identical deduction in RC-space uses seven cells -- instead of five "hidden cells" -- it should be no surprise that it also uses five strong inferences.

Code: Select all: 4 3 257 | 68 1 567 | 56 268 9 26 *79 1 | 689 2369 *57-369|*45-6 *2468 268 268 89 258 | 4 269 569 | 7 3 1 ------------------+-------------------+----------------- 28 6 28 | 5 7 1 | 3 9 4 1 5 9 | 3 68 4 | 2 68 7 7 4 3 | 2 689 69 | 1 5 68 ------------------+-------------------+----------------- 3 2 6 | 7 4 8 | 9 1 5 5 *17 *47 | 169 369 369 | 8 *246 26 9 18 48 | 16 5 2 | 46 7 3 r2c2 =7= r2c6 =5= r2c7 =4= r2c8 -4- r8c8 =4= r8c3 =7= r8c2 -7- loop, implies r2c6<>369, r2c7<>6

Website · by **denis_berthier** » Sat Aug 25, 2007 6:54 am

Several persons asked for a program that could display automatically the rn- and cn- representations. Ruud has announced in the UK forum that they are now integrated into his last release of Sudocue.
I hope this will help those of you who want to try them.

Beware, I never said they are a panacea. But they can make some puzzles easier to solve.
Remember that what you can do in these representations is simple: anything that you do in the other representations and that does not use the notion of a block, e.g.
- subsets (hidden subsets and fishy patterns will appear as mere naked subsets),
- xy-, xyt- and xyzt chains.

by **re'born** » Sat Aug 25, 2007 9:37 am

denis_berthier wrote:Beware, I never said they are a panacea. But they can make some puzzles easier to solve.
Remember that what you can do in these representations is simple: anything that you do in the other representations and that does not use the notion of a block, e.g.
- subsets (hidden subsets and fishy patterns will appear as mere naked subsets),
- xy-, xyt- and xyzt chains.

If you're careful, even some techniques that use blocks can be used. For instance, sashimi and finned fish and even some of the uniqueness techniques can be spotted with corresponding moves in RN or CN space.

Website · by **denis_berthier** » Sat Aug 25, 2007 12:12 pm

re'born wrote:If you're careful, even some techniques that use blocks can be used.

If you are careful, yes. But not for first users.

The New Sudoku Players' Forum

Supersymmetries and Hidden chains

Automatic display of the rn- and cn- representations

Re: Automatic display of the rn- and cn- representations

Re: Automatic display of the rn- and cn- representations