(IUCr) Hexagonal direction indices

Figure 6
The coordinate system ( $[\xi_1^{o},\xi_2^{o},\xi_3^{o}]$ ) is obtained from the coordinate system ( $[\xi_1,\xi_2,\xi_3]$ ) through a counterclockwise rotation by an angle [pi]

/6. The new axes $[\xi_1^{o}]$ , $[\xi_2^{o}]$ , and $[\xi_3^{o}]$ are aligned along the close-packed atomic directions of interatomic spacing a₀.