The first two levels are restored together. There are many ideas and types of formulas here

The 41 standard formulas basically have no core ideas and need to be memorized by heart.

The bug's f2l formula is based on the idea of ??restoration. You will understand it after taking a look at it.

On average, a group of restorations can be restored in 6-8 steps, which is still very good.

I know you use your mobile phone, so I will bring you the bed bug stuff, but it’s a bit awkward without a picture.

I played the entire F2L by myself, so I have a relatively deep understanding of F2L, and my results on the first two levels are pretty average. There are many web pages about F2L on the Internet, but most of them do not explain it. This article attempts to give some simple explanations, hoping to be of some help to the newbies who are learning F2L, haha.

The main content and viewpoints of this article were written down when I was studying F2L seven years ago. However, the draft at that time was long ago thrown away, and it took a lot of effort to finally get it out again. F2L focuses on understanding. Many formulas can be used naturally once you understand them. This article divides all 41 F2L into three forms according to your own understanding, and classifies the formula reduction ideas in F2L in order to explain some of the rules of F2L. .

First of all, let me talk about my classification of formula reduction ideas in F2L. I divide this into two categories. The first type I call ordinary ideas. The core of the idea is to maintain the integrity of the first two layers to the highest degree throughout the entire formula process. That is, during the entire reduction process, there are no two or more Corners (including completed and unfinished) participate in the top layer at the same time. Only one of the four blocks of the bottom cross is always in a non-reduction state. The step structure is as follows: adjust the top layer---corners participate in the top layer- --A rotation of the top layer---New corners return to the bottom layer---Other corners join the top layer... The second type is what I call the direct restoration idea, which is an idea that does not care about whether the first two layers are complete during the restoration process, but directly restores it in the most recent way.

The formulas of ordinary ideas are usually very simple and direct. Once you understand them, you will basically never forget them. At the same time, they are extremely flexible and the techniques are simple. They occupy a major position in F2L, such as the Rubik's Cube tutorial. Among the 41 F2Ls, 29 belong to this kind of restoration idea. The disadvantages of the direct restoration idea are that it is more complicated, requires some memory, and generally lacks flexibility. There are also some application restrictions. Its advantage is reflected in its number of steps, which is higher than that of the ordinary idea. The formula has some advantages. In addition, the formula that directly restores the idea often flips the bottom surface to the top surface during rotation, so it actually has the effect of changing the field of view.

Having talked about the idea of ??formula reduction, here I will talk about my classification of 41 F2L graphics.

If you use the ordinary restoration idea to rotate, the two graphics A1 and A2 in the following table are the first changes in the "restoration state". They are formed by a process of "corners participating in the top layer---a rotation of the top layer---new corners returning to the bottom layer". They are the simplest change of the restored state, that is, the first change. Continuing this step, the secondary and tertiary changes of the reduction state will also be produced. All F2L graphics can be simply classified as the primary, secondary and tertiary changes of the reduction state. They respectively represent the three changes of F2L. Difficulty levels.

Secondary forms include the following B1, B2 graphics, etc. If these types of graphics are restored using ordinary ideas, it will require two processes of "converting to the primary form---converting to the restored form", which generally requires Steps 6-8. If you use the direct reduction method to restore, it usually takes steps 6-7. Tertiary forms such as C1, C2, etc. If these types of graphics are restored by ordinary methods, they require three processes of "converting to the secondary form---converting to the primary form---converting to the restored form", which usually takes 9 -12 steps, while the direct restoration method usually requires 8-9 steps.

This kind of classification is very suitable for beginners to proceed step by step. The three changes of the restored form are inherited and changed. It will be easier to understand and get started if you follow the learning.

It should also be noted that the formula that directly restores the idea will have application limitations under certain conditions. This restriction only exists if one or two of the missing corners or edges are in the underlying graphics (***9: B1-B5, C2-C5).

The conventional F2L formula in these figures places the missing corners and edge blocks in their original positions (what I call it refers to the relative position of the Rubik's Cube blocks when they are restored to their original state. Including when it is rotated at this position), the restoration effect is to restore the defective block directly to the defective corner. However, in actual situations, the majority of cases are that the missing blocks are not in their original positions. For these cases, if these formulas are still used to deal with them, erroneous restoration will occur.

This article colors the formulas to distinguish various types of formulas: green formulas represent formulas with common ideas. These formulas are simple and flexible, without any restrictions. Anyone who has time may wish to learn them all, which will help improve overall ability. It is very beneficial; the blue-gray formulas represent direct reduction ideas without application restrictions, and the blue ones are those that I think are relatively simple and easy to remember or have a particularly small number of steps; the black formulas represent direct reduction ideas with application restrictions. The formulas in red are ones that I think are relatively simple and easy to remember or have very few steps. It is not recommended to learn too many formulas. Except for the six figures B11 and C1-C5, there is actually no need to learn the formulas that directly restore the idea.

Previous note:

1. Most of the following figures have several formulas to solve. Except for the two basic formulas A1 and A2, as a beginner, each figure only has Just learn a formula. You can choose the simplest and easiest one or the one with the least number of revolutions, but it must not be a formula with restrictions on use. For each of the following figures, I will indicate the name of the figure in the Rubik's Cube F2L tutorial in brackets after the name of the figure. The number after the dash indicates that the formula under the figure is the formula recommended in the Rubik's Cube F2L tutorial. This list is for reference by learners. In addition, the first formula under each graph is the simplest and easiest formula in my opinion, and is for reference by lazy people.

2. This article is quite special in the statistics of revolutions and the writing of formulas. In addition, the generally mentioned 41 F2L formulas actually include symmetrical or repeated graphics, and there are actually only 22. This article will only select one of the repeated figures and list them, and the symmetrical formulas will not be repeated in this article. There is a list of symmetrical figures attached at the end of this article, you can take a look.

1. One-time change form (2 types)

A1 (I1-1)

A2 (T1-1)

< U'>F' U F (3-1)

F' U2 F (3-1)

F R' F' R (4-1) R U R' ( 3-1)

There are only two forms of change at a time, which are the most basic forms in F2L and play the most important role in F2L. The latter part of many F2L formulas actually apply these two formulas. Learning these two F2Ls first can help you learn other F2Ls later more easily. It is strongly recommended to learn all four solutions.

In the above figure, the parentheses before the formula indicate the adjustment steps, because it is undetermined where the top-level block will appear, and these steps may or may not be needed. The number listed after the formula represents the number of steps of the formula. There are two values ??in the column. The first number represents the number of steps of the pure formula, and the latter number is the number of adjustment steps that may be needed to clearly compare the true state of the steps. .

Second, secondary change forms (15 types)

1. The situation where the corners are on the bottom layer and the edges are on the top layer (3 types)

These three shapes It is relatively easy to learn in F2L except for the two basic figures A1 and A2. The first figure is actually the middle-level formula in the conventional layer-first method. If you are already proficient in A1 and A2, you only need to use a little spatial imagination. It is easy to imagine the solutions to these three graphics. The basic key point of cracking these three graphics is to use the corner block to form the edge block. According to the shape of the corner block, simulate the shape of A1 or A2, rotate the top edge block to a certain position, and then move the corner block to form the top edge block.

B1 (A1-1)

B2 (E2-2)

B3 (F2-2)

R U ' R' (A1 6-2)

R U R' (A2 6-2)

R U2 R' (A2 6-2)