mark backside of the paper strips with bI/II,i1I/II,a1I/II,...,a9I/II,eI/II
square diagonals: valley folding, paper strips: alternative mountain-/valley folding
plaiting scheme:
a1 a2 a3 a4 a5 a6 a7 a8 a9
I ↑↑ i7 II ↑↑ i3 II ↓↑ i8 I ↑↑ i1 II
↑↑ i6 II
↓↑ i2 I ↑↑ i4 II ↑↑ i9 II ↓↑ i5 I
II ↑↑ i1 I ↑↑ i6 I ↓↑ i8 II ↑↑ i4 I
↑↑ i9 I
↓↑ i2 II ↑↑ i7 I ↑↑ i3 I ↓↑ i5 II
start with a2I↑↑i3II, a8II↑↑i3I, a3II↑↓i8II,
a2II↑↑i6I, a6I↑↓i2I, a7II↑↑i7I, a7I↑↑i4II, a3I↑↓i8I, ...