for example, the point group for the water molecule is c2v, with symmetry operations e, c2, σv and σv'. its order is thus 4. each operation is its own inverse. as an example of closure, a c2 rotation followed by a σv reflection is seen to be a σv' symmetry operation: σv*c2 = σv'. (note that "operation a followed by b to form c" is written ba = c).