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This thread has one and only one topic: the BpB classification of T&E(2) puzzles, with its possible correlations (or not) with other ratings, such as the SER.
1) INTRODUCTION
The discovery of the Loki puzzle by mith and my discovery that it was in T&E(3) (http://forum.enjoysudoku.com/the-hardest-sudokus-new-thread-t6539-1048.html) have led to a sudden surge in the number of "potentially hard" puzzles.
This has also led to splitting the old "hardest" thread (http://forum.enjoysudoku.com/the-hardest-sudokus-new-thread-t6539.html) into two threads:
- a new one dedicated to finding T&E(3) puzzles: http://forum.enjoysudoku.com/t-e-3-puzzles-split-from-hardest-sudokus-thread-t40514.html;
- the same old one with a now explicit goal of looking for SER-hardest puzzles and excluding puzzles in T&E(3), which turns it de facto into a thread dedicated to finding T&E(2) puzzles with highest SER.
In the same way as I introduced a thread (http://forum.enjoysudoku.com/the-tridagon-rule-t39859.html) to analyse the puzzles found in the T&E(3) one, I'm now introducing the present one to analyse the puzzles found in the T&E(2) one.
2) THE BpB SUB-CLASSIFICATION OF T&E(2)
The T&E(T, n) procedure and the BpB classification of T&E(2)=T&E(Singles, 2) puzzles were introduced in my book [CRT, 2011] and reproduced in all the subsequent editions of my book [PBCS].
The BpB classification relies on an easy theorem proven in [CRT]: a puzzle P can be solved in T&E(1) iff it can be solved by braids, i.e. by braids[≤p] for some maximal length p (depending on P).
This trivially implies the following theorem:
- a puzzle P can be solved in T&E(2) iff it can be solved by B-braids, i.e. by Bp-braids of any total length but for some maximal value of p (depending on P).
This defines a sub-classification of all the puzzles in T&E(2) - and the associated BpB rating (the smallest p such that P is in BpB).
T&E(2) is the disjoint union of all the T&E(Bp, 1) (also named BpB for obvious reasons), for p=1, 2....
(Note B0B=B=T&E(1)).
3) THE B7B CONJECTURE
I also showed in [CRT] that all the known puzzles in the currently "hardest" database were indeed in BpB, for some p ≤ 7. Which became my B7B conjecture. This was reproduced and updated in every edition of [PBCS].
With the discovery of Loki and it being in T&E(3), my T&E(2) and B7B conjectures (which had hold for more than 12 years) were falsified. From that time on, I also stopped checking systematically all the newly discovered high SER puzzles.
However, there remains a modified conjecture: all the puzzles in T&E(2) are indeed in BpB for some p ≤ 7.
[Notice that I've proven that all the known puzzles in T&E(3) are indeed in B2BB (BpBB defines a similar sub-classification of T&E(3) (see the T&E(3) thread).]
This doesn't imply that the modified T&E(2) conjecture is the topic of this thread, but it's clearly part of it. In any case, it'd be interesting to know how high p can be.
References:
[CRT, 2011]: https://www.researchgate.net/publication/280301602_Constraint_Resolution_Theories
[PBCS1, 2012]: https://www.researchgate.net/publication/280301697_Pattern-Based_Constraint_Satisfaction_and_Logic_Puzzles
[PBCS2, 2015]: https://www.researchgate.net/publication/280100555_Pattern-Based_Constraint_Satisfaction_and_Logic_Puzzles_Second_Edition
[PBCS3, 2021]: https://www.researchgate.net/publication/356313228_Pattern-Based_Constraint_Satisfaction_and_Logic_Puzzles_Third_Edition
Note that I gave many definitions on this forum before formally publishing them in the above references.
[Edit "2024 May 2"]:
In order to avoid any confusion between the BpB classification and the BpB rating of a puzzle, the BpB classification has been renamed BxB classification. This is more consistent with the common usage that x is the unknown. Similar changes have been made to the BpBB classification (now BxBB classification).
Reminder:
- in "BxB classification", the "x" is the value to be found for the puzzle.
- in "BpB rating", p is fixed and what's to be found is the minimal length of Bp-braids necessary to solve the puzzle.
In any post posterior to this date, I'll use this new notation. I'm too lazy to change all the posts.
The changes have also been made in the SHC.
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