Insertions
The leftover corners, cycled at the best point.
Insertions
Three leftover corners are solved by a commutator, a short sequence that cycles exactly those corners. Inserted at the end of the skeleton it costs its full length; inserted at the right point inside the skeleton, with the cycle it needs there, it can cancel moves on both sides. Fewest-moves solvers check every point of the skeleton for the insertion that cancels most. The last-layer forms of these cases are the L3C set.
[R U R', D]
A corner commutator: R U R' D R U' R' D' cycles three corners and nothing else. (8 HTM)
Checked by the engine: [R U R', D] → 3 corners moved, 0 edges moved, 0 centers moved