The pseudo-symmetry often occurs in the crystal structures. The types of pseudo-symmetry may be classified into three categories, i.e. enantiomorphous, translational and those based on other symmetry elements. The present paper discussed some possible translational types in detail, and derived the elements of the pseudo-symmetry for the low symmetry crystal systems (74 space groups). A number of examples show that the pseudo-symmetry is universally exist. Finally, the compatibility between the pseu-do and inberent symmetry groups is also discussed.
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