F2L reductions
Lots of F2L algorithms aren't learned from scratch - they start by turning a harder case into an easier case you already know, then solve that. That shortcut is a reduction, and the F2L database can show it instead of the raw move list.
A worked example
Take this algorithm for the case below. Watching only the two pieces you're solving, partway through it becomes a simpler case:
The first three moves - R' U R - leave the pair in this easier case, which you finish with a basic R U R':
So the database lists this as a reduction: do R' U R, then it's the
easier case - no need to memorise the whole string as one block.
The “Reduce to easier cases” toggle
- On (default): an algorithm that reaches an easier case shows the moves up to that point, then the easier case's picture and name. Hovering the row reveals the finish - the easier case's most-used algorithm (aligning U-turn included), or, on an unfolded row, that algorithm's own continuation. Click the picture to open that case's own page.
- Off: every algorithm is shown in full, as one move sequence.
Reductions are great for learning: if you already know the easier case, you only have to remember the short setup in front of it. The “Fold same reductions” option then groups the algorithms that share a setup into the same easier case onto one row - they only differ in how they finish that case.
Rotation reductions
Sometimes the “setup” is nothing but a cube rotation: turn the whole
cube (y, y', d or d') and you're suddenly
looking at a case you already know - just in a different slot. No pieces
move at all; it's the same position viewed from another angle.
Which of those rotations you pick only changes your grip, not the solve, so they're interchangeable. That's what the “Fold rotations” option (on by default) does: every algorithm that reaches the same easier case by a pure rotation is grouped into a single row with a generic rotation chip, with their usage and votes summed. Turn it off to see each specific rotation as its own row.