The successive application (or composition) of one or more symmetry operations of a molecule has an effect equivalent to that of some single symmetry operation of the molecule. For example, a C 2 rotation followed by a σ v reflection is seen to be a σ v ' symmetry operation: σ v * C 2 = σ v '. ("Operation A followed by B to form C " is written BA = C). Moreover, the set of all symmetry operations (including this composition operation) obeys all the properties of a group, given above. So (S, *) is a group, where S is the set of all symmetry operations of some molecule, and * denotes the composition (repeated application) of symmetry operations.