The Trap DIY method

Method 'DIY'; Step 4 Layer 3

This is the trickiest configuration the cube can have: the OY and YG cubies swapped. (More generally: 2 cubie swapped.)

Contrary to what may seem, on the third layer, each cubie can only occupy 2 out of the 4 available positions, otherwise the configuration became impossible to solve.

Once the OY and YG cubies are placed, attention turns to the other two cubies (the RY and BY), and all efforts are focused on how to position them correctly.

Here lies the deception: it is the two cubies, OY and YG, in the wrong position that prevent the other two cubes, RY and BY, from reaching their places."

However, the solution could not be simpler: a single clockwise or counter-clockwise rotation of the Yellow face is what needed. (look the comment inside move 1.)

This configuration is also analyzed in the section Method 'Workbench' The Trap and the section 'Extras' The Trap

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1)	U'	Brings the RY cubie to its correct position. This simple rotation is the key. Now, on the yellow face there are one cubie correctly positionated: the edge RY and three cubies not in the correct position. The 'sledgehammer' can order 3 edges, so now the configuration is solvable again. Perhaps this other point of view can help. Given this sequence: 1 2 3 4 - with a rotation of 4 elements it becomes ('4' goes in the 1st place): 4 1 2 3 - with a rotation of the first 3 elements it becomes ('4' goes in the 3rd place): 1 2 4 3 - the 3rd and the 4th number are swapped. Combining rotations of 4 and 3 elements it is possible swap 2 elements in a sequence. - the rotation U' is a rotation of 4 elements. - the sledgehammer is a rotation of 3 elements. These are the 2 rotation that combined made the cube solvable.
Now the cubie YG must be restored to its correct position.
2)	U2	Places the cubie YG onto the 'workbench' (the 3 branches of the 'Workbench') To let the next 'sledgehammer' restore the correct position of the cubie YG. The choice of the YG cubie is actually mandatory because now we need to bring the OY and YG cubies closer to the RY cubie. To prevent these operations from interfering with each other, it is necessary to start with the YG cubie. Sould be pretty clear that the move number 2 (this move) cancels the previous move (the move number 1). The reason they are kept anyway is because they belongs to 2 different reasoning: - The first move makes evident that the rotation U' changes an 'impossible configuration' to a configuration that can be easily solved (in the context of the sledgehammer) - the second (the rotation U2) is just the beginning of the next task: move the cubie YG to its correct position.
3)	U   F'	Moves the cubie OYG anywhere else on the workbench. So that the face orange can be resrored (rolled back).
Now it is the cubie OY that must be restored to its correct position.
4)	U	Brings the RY cubie to its correct position.
5)	U   F'	Moves the cubie OYG anywhere else on the workbench. So that the face orange can be resrored (rolled back).
6)	U	Brings the RY cubie to its correct position.