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Systematic absences

One speaks of systematic absences or extinctions when the structure factor is zero, due either to the centering of the lattice or to the presence of glide or screw symmetry elements. Conversely, the  conditions  for a reflection to exist and not to be systematically absent, are  called  reflection conditions.

See also

Sections 2.2.13 and 12.3.5 of International Tables of Crystallography, Volume A