25 HTM Official Solve by Guus Razoux Schultz @ Twente Open 2012

Scramble: D L2 D’ R2 B2 D’ U’ B2 L’ F’ R D’ U’ F2 U B F’ L2 B2 U2
Solution: L2 U2 D B U2 B’ D2 B U2 L R’ D2 F R F’ U F U2 R U F R2 F2 D’ B’ (25 HTM)

Explanation / Comment:
I chose [B’] as pre-scramble move on the normal scramble. Why? I Explain later.
2x2x2 block: U2 D’ B L
not happy with continuation so I searched for inserted moves, possibilities: L, L2 and L’ before first move. L2 worked out best:
so: 2x2x2 block: L2 U2 D’ B L (5+1)
pseudo 2x2x3: R’ D2 (7+1)
undo pseudoness with extra pre-move D’ (7+2)
So premoves [D’ B’] F2L-1: F R2 (9+2)
switch to the inverse scramble with this start as pre-moves: [R2 F’ D2 R L’ B’ D U2 L2]
F2L-1: B D (2+9)
many possibilities to finish f2l, I chose for most cancellations on next step (ELL)
F2L: F2 R2 F’ R2 F R (8+9)
ELL: R’ F’ R2 U’ R’ U2 F’ U’ F R (12+9) — 6 moved cancelled!
again one move cancelled with pre-move correction which gave the following edge frame with 3 corners left:
B D F2 R2 F’ U’ R’ U2 F’ U F R R2 F’ D2 R L’@ B’ D U2 L2 (20)
at @ insert U2 B’ D2 B U2 B’ D2 B, 3 moves cancel
inverting the solve gives the solution above

Why did I choose B’ as pre-move in the beginning? Let me explain.
– 3 moves make a pair on the regular scramble ( U’, R2 and L’)
- 5 moves make a pair on the invere scramble ( U, R, R2, L, and B)
Because each “pairing-move” can also be used a pre-scramble-move, there are 16 ways to start with a 1-move-pair.
These are simple too much possibilities to investigate, so I had to pick only a few of them.
Then I had a look at number of the bad pairs after the scramble. Bad pairs are adjacent corner-edge pairs that are wrongly paired up. This scramble had 6 bad pairs. Which is about average.
I chose B on the inverse scramble and B’ as pre-move on the inverse scramble because this move unlocked 2 bad pairs while all other pairing-moves did not unlock any bad pair.
This tactic is based on the assumption that less bad pairs in a scramble are possibly easier too solve, at least easier to find a good block build.
I cannot prove this, purely intuitive assumption.
Since three months or so I use this trick to prevent getting lost in too many, good or bad, possible starting moves.
And this time it worked out very well.

Happy with this, a PB-2, I never did so many tricks in a competition solve. ;-)

Original post

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