摘要: Basic symmetry properties of transformation twins and ferroelectric or ferromagnetic domains are examined in terms the abstract group theory. It is shown that crystallographical relations between (twin components) domain pairs can be deduced from decomposition high phase into left double cosets low phase. Expressions derived for numbers proper improper domains, number crystallographically equivalent phases, non-equivalent pairs. A classification according to their proposed. The structure monoclinic WO3 Dauphine twinning quartz analysed as illustrative examples.