#### ottozing

##### Platinum Member

The idea with ROLL starts with knowing what type of CP you'll get after your OLL alg. It'll either be diagonally permuted corners (E perm, N perms, Y perm, V perm), solved coners (U perms, H perm, Z perm), or adjacently swapped corners (The other 11 PLL cases). Doing that alone is very easy if you have already learned CP recognition from something like CLL on a 2x2, or COLL for 3x3, and have played around a bit with how CP cases correspond to other CP cases (For example, F R U R' U' F' gives a diagonal PLL for when R' U' R U' R' U2 R2 U R' U R U2 R' solves corners, and vise versa). With that said, that's not 100% what ROLL is about. With ROLL, when you know you're going to get an adjacent corner PLL, you also know where the headlights are going to be.

As you can probably tell, this requires knowing your OLL's a lot better than you would need to for just narrowing down the 3 types of corner permutations to one, but it can definitely come in handy. I can't speak for anyone else, but with my PLL algs, most of the adjacent corner PLL algs have the headlights on the left (Only one of the R perms, and the A perms don't). If I can immediately AUF after OLL so that the headlights are on the left, then that can help most of the time, although that's a ridiculous amount to learn for considerably little gain. However, learning to associate CP cases for certain OLL's with the headlights going to be on the left is very nice, because that leaves room to possibly cancel into your PLL alg.

I mentioned earlier the idea of playing around with what CP cases correspond with other ones, but in particular, knowing the opposite CP to every CP case (Opposite meaning the one where the alg which would normally solve CP would give diagonal CP), is very useful for ROLL in two ways. The first way is that if you know an OLL case has the opposite CP for the alg you usually use, you can narrow down your possible PLL case from 21 to 5. The other much less obvious way in which it's useful is for when you see an OLL with a CP that's the opposite of what would usually give headlights on left. When you see that, you know that if you do a U2 after OLL, you'll put headlights on left, and likely set up your PLL into the position it should be in.

I'll post some examples later (Some with ROLL, and some with both ROLL and the edge recognition method thing, just to show how much the possible PLL case can be narrowed down, along with a point I want to make about a certain ROLL+edge case).