I'm trying to solve a 4x4x4 rubiks cube. I've finished the middle and side pieces so I can solve it like a 3x3x3 but I'm stuck on the penultimate step - positioning the final corners. The instructions say: "Due to the parity the amount of the correctly positioned yellow cubelets is limited to three cases: there's no yellow corner piece in the correct position, or there's only one, or all the four pieces are correct." But I have 2 corner pieces solved which should be impossible. Is there anything I can to to solve it?
There are a couple of possibilities.
- You actually do have all the corner pieces in the correct places. Depending on the method you are using, the pieces don't necessarily have to be correctly oriented yet, so they may look like they are in the wrong place. Check if twisting the offending corners in place would solve them, and if so, you are good to continue.
- There is another misplaced corner on the opposite (white) side. Start over from that step to fix.
- You have an unsolvable cube, with six corners in their correct places, and the remaining two swapped with each other. This can only happen if your cube has been taken to pieces and reassembled incorrectly. It's impossible to swap only two corner pieces with each other by twists of the cube, so you'll have to take the cube apart and reattach the pieces in the correct configuration. To disassemble the cube, twist the top layer 45 degrees and insert a flat screwdriver tip (or a thin fork handle, or what have you) under the rotated layer, and apply a little pressure to pop a piece out. The rest of the cube will come apart a lot easier.
Hope this helps!