Module class_group

The class group of a number field.

EXAMPLES:
    sage: K.<a> = NumberField(x^2 + 23)
    sage: I = K.class_group().gen(); I
    Fractional ideal class (2, 1/2*a - 1/2)
    sage: J = I * I; J
    Fractional ideal class (2, 1/2*a + 1/2)
    sage: O = K.OK(); O
    Maximal Order in Number Field in a with defining polynomial x^2 + 23
    sage: O*(2, 1/2*a + 1/2)
    Fractional ideal (2, 1/2*a + 1/2)
    sage: (O*(2, 1/2*a + 1/2)).is_principal()
    False
    sage: (O*(2, 1/2*a + 1/2))^3
    Fractional ideal (1/2*a - 3/2)