ryokousha wrote:This is a 20 cell minimal arising from those. We have not yet found any proof that this can't be 4-colored.
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X X . | X . . | X . .
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..................11.1..1........1...1.1..1..11..1...1.1..111..1..1.....1..1.....
This pattern can be proven contradictory in T&E(2), more precisely in T&E(BC2, 1):
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(solve-k-digit-pattern-string 3 "..................11.1..1........1...1.1..1..11..1...1.1..111..1..1.....1..1.....")
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! 123456789 123456789 123456789 ! 123456789 123456789 123456789 ! 123456789 123456789 123456789 !
! 123456789 123456789 123456789 ! 123456789 123456789 123456789 ! 123456789 123456789 123456789 !
! 123 123 123456789 ! 123 123456789 123456789 ! 123 123456789 123456789 !
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! 123456789 123456789 123456789 ! 123456789 123456789 123456789 ! 123 123456789 123456789 !
! 123456789 123 123456789 ! 123 123456789 123456789 ! 123 123456789 123456789 !
! 123 123 123456789 ! 123456789 123 123456789 ! 123456789 123456789 123 !
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! 123456789 123 123456789 ! 123456789 123 123 ! 123 123456789 123456789 !
! 123 123456789 123456789 ! 123 123456789 123456789 ! 123456789 123456789 123456789 !
! 123 123456789 123456789 ! 123 123456789 123456789 ! 123456789 123456789 123456789 !
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609 candidates, 8514 csp-links and 8514 links. Density = 4.6%
GENERATING CONTEXT 1 AT DEPTH 1, SON OF CONTEXT 0, FROM HYPOTHESIS n3r9c4. <<< This is level 1 of T&E, in which BC2 is used.
biv-chain[2]: r8c4{n1 n2} - r5c4{n2 n1} ==> r7c4≠1, r3c4≠1, r2c4≠1, r1c4≠1, r6c4≠1, r4c4≠1 (this is also a Naked Pair).
singles ==> r3c4=2, r8c4=1
NO POSSIBLE VALUE for csp-variable 154 IN CONTEXT 1. RETRACTING CANDIDATE n3r9c4 FROM CONTEXT 0.
BACK IN CONTEXT 0 with 0 csp-variables solved and 608 candidates remaining. Only regular whips (in T&E(1)) are required to finish the proof.
whip[3]: r9c4{n1 n2} - r7c5{n2 n3} - r7c6{n3 .} ==> r9c6≠1
whip[3]: r9c4{n1 n2} - r7c5{n2 n3} - r7c6{n3 .} ==> r9c5≠1
whip[3]: r9c4{n1 n2} - r7c5{n2 n3} - r7c6{n3 .} ==> r8c6≠1
whip[3]: r9c4{n1 n2} - r7c5{n2 n3} - r7c6{n3 .} ==> r8c5≠1
whip[3]: r9c4{n1 n2} - r3c4{n2 n3} - r5c4{n3 .} ==> r8c4≠1
z-chain[3]: r8c4{n2 n3} - r5c4{n3 n1} - r9c4{n1 .} ==> r1c4≠2, r7c4≠2, r6c4≠2, r4c4≠2, r3c4≠2, r2c4≠2
biv-chain[3]: r9c4{n2 n1} - r3c4{n1 n3} - r8c4{n3 n2} ==> r5c4≠2, r7c5≠2, r7c6≠2, r8c5≠2, r8c6≠2, r9c5≠2, r9c6≠2
biv-chain[2]: r5c4{n3 n1} - r3c4{n1 n3} ==> r4c4≠3, r6c4≠3, r7c4≠3, r8c4≠3, r1c4≠3, r2c4≠3
singles ==> r8c4=2, r9c4=1, r3c4=3
PUZZLE 0 HAS NO SOLUTION : NO CANDIDATE FOR RC-CELL r5c4