Figure 9.2.2.2 

Schematic representation of three structures belonging to the OD groupoid family P(1)m1|1, y = 0.25 (left). The layers are perpendicular to the plane of the drawing and their constituent atomic configurations are represented by isosceles triangles with symmetry [.m.]. All structures are related to a common orthogonal four-layer cell with a = 4a₀. The hk0 nets in reciprocal space corresponding to these structures are shown on the right and the diffraction indices refer also to the common cell. Family diffractions common to all members of this family (k = 2) and the characteristic diffractions for individual polytypes (k = 2k + 1) are indicated by open and solid circles, respectively.