Figure 8
(a), (b) Non-equivalent ditetragonal (bi)-pyramids {29l}ditetr (green) and {67l}ditetr (red), both with h2 + k2 = 85, i.e. equal d values. (c) Mono-tetragonal (bi)-pyramids {29l} (green) and {67l} (red). The twin elements m' do not belong to the eigensymmetries of these subforms, but map them upon each other. Thus, the corresponding reflection subsets are coincident but have different F moduli (diffraction case B1). (d) Associated mono-tetragonal (bi)-pyramids {92l} (green) and {76l} (red). These subforms are not mapped upon each other: the corresponding reflection subsets are `single'. This `partial coincidence' holds for all general ditetragonal sets {2h.9h.l} and {6h.7h.l} (except for the pedion/pinacoid, h = 0). The same coordinate system is used for all reflections.  [article HTML]

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