Keyhole First Two Layers or Keyhole F2L, sometimes named working corner, is a method that solves, normally, the first two bottom layers of the 3x3x3 cube. It is an efficient method for inserting mid-layer edges in the 3x3x3 LBL method. Its a slight advancement on the basic LBL method, because it requires fewer moves, as well as more intuition.
After the bottom layer cross, only three bottom layer corners are solved. The final corner is reserved as the keyhole to be used in solving the mid layer edges efficiently. To insert a mid layer edge using the keyhole:
You start, like in normal LBL from a cross, then you fill in three of the first layer corners. From that point you solve three of the middle layer edges using the empty corner position as the keyhole. For each edge do the following:
- First position the mid-layer edge in the U-layer such that it is above the centre matching the edge's up-facing colour.
- Using a D-Turn position the bottom layer so that the unsolved corner is directly below the mid-layer edge's position.
- Now execute one of R U' R' or F U F' to insert the edge.
After three corners and edges are solved you complete F2L by first solving the last corner and finally the last edge using the normal LBL algorithm: R U R' U' F' U' F or the mirror F' U' F U R U R' depending on the current orientation of the edge.
An alternative way to do keyhole F2L is to use this order:
- cross (doesn't have to match centers)
- 3 corners
- 4 edges
- 4th corner
For that you will need three algorithms to solve the last piece depending on it's orientation:
List of algs...
|F2L||(R U R' U')(R U R' U')(R U R')|
|F2L||(U R U' R')(U R U' R')(U R U' R')|
|F2L||U2 R d' R U R' d R'|
|F2L||U R d' R U2 R' d R'|
|F2L||R2 U R2 U R2 U2 R2|
|F2L||U2 R2 U2 R2 U' R2 U' R2|
|F2L||(U' R U' R') U2 (R U' R')|
|F2L||y U' (L U' L') U2 (L U' L)|
|F2L||U' (R U2' R') U (R U R')|
|F2L||U (R U R') U2 (R U R')|
|F2L||d (R' U R) U2 (R' U R)|
Another way to approach keyhole is to start by inserting three edges, and then use the remaining unsolved edge position to insert three corners. The basic steps are as follows:
- Solve Cross
- Solve 3x E-slice edges
- Rotate cube to position remaining unsolved slot in FR
- Solve 3x D-layer corners by:
- Position a D-layer corner above the slot in the U-layer
- Rotate D-layer so that the corner's correct location is directly below the slot
- Insert the corner using one of: R U R' or F' U' F or R B U2 B' R'
If there are no corners available in the U-layer, then rotate the D-layer until an unsolved D-layer corner is above the slot, and then use R U R' to swap it into the U-layer.
While both the corners and edges first approaches use a similar number of moves, edges-first does not require the solver to keep track of the working corner, which can be better for lookahead. If used in conjunction with 8355 it may also improve ease of understanding, since a similar concept is used to place the final 5 corners.