ZZF2L Pair Choice
By yoruba
Pair choice is the skill of seeing multiple pairs to solve and choosing the best one. ‘Best’ might not always mean choosing the fastest pair to solve immediately, as it may influence the other pairs to be worse. This is a very important aspect of F2L.
In this example, there is a 3-move pair and a 4-move pair. If we chose the 3-mover first, the 4-move pair becomes much worse:
Moves:(R U' R') U' (R' U' R U' R' U R)
But if we choose the 4-mover first, the 3-mover is preserved. This is 4 moves shorter!
Moves:(U' R' U' R) U (R U' R)'
It’s the transition of looking at F2L not as 4 individual pairs (intermediate approach), but as one step (advanced approach) that will save you the most time.
Prerequisites
In order to consider pair choice, there are some prerequisites:
- Optimize pair solutions beforehand. If you don’t do that, chances are that most of the time all of your choices would be equally as bad.
- Look at a pair, and immediately know the solution, as well as the quality of that solution. You can categorize them into 3 cases: free pairs/3 movers, 6-7 movers (pieces in U), and the rest.
- Deduction (learn more here)
Developed through focused untimed f2l only solves, practice by trying out different things, looking for patterns and make sure you’re aware of all of your F2L pairs.
Rules of thumb
- Prioritize free pairs and easiest pairs.
- Look out for the U layer: if an f2l case has an F2L piece in U, it’s most likely good.
- Pair order: solve back/right/left slots first.
Pair order
It’s preferable for your first F2L pairs to be BL+BR (back slots), BL+FL (left slots), or BR+FR (right slots). This will ensure that you will have all of your pieces visible, as well as it will make sure that your last two pairs will be fastest on average. That means you should be avoiding solving both front first, or slots that are diagonal (FL+BR, FR+BL) which interfere with lookahead and turning.