huinventors1-3, Exercise 2: The five stages

Model answer:

1. First-layer cross: place four edges around one centre, matching the side colours.
2. First-layer corners: insert the four corners with a short repeated sequence.
3. Middle layer: insert the four middle edges with a pair of mirrored sequences.
4. Last-layer cross: make a cross on the opposite colour.
5. Last-layer corners and edges: position and orient the remaining pieces with short sequences.

The linking idea is the algorithm: a fixed sequence of moves that does one small job and preserves what is already solved, so each stage builds on the last without undoing it. Details of how stages are taught vary and should be checked.