[up to this 3D shape]
- Start from
- Locate a sequence of four consecutive tiles (A, B, C, D) hinged about
parallel sides and foldings of (in order) valley, valley, mountain type
- By slightly opening the structure change the folding between B and C
from valley to mountain, tiles A and B are stacked together in the process
- Turn the newly formed flap 90 degrees into the final shape
