Solving Big Cubes by Logic
4.f. Solving up to 3 corners of the first layer and leaving one “free”
This step is straightforward: solve three corners of the first layer. If the cube is even, solve one additional corner as two were already solved in step "4.b". The "go, swap and back" movement is sufficient, as it is well-known in the 3x3x3 solution.
One corner is intentionally left unsolved to maintain the same "free column" for the "go, swap and back" moves from the previous step.