 We can now define the quotient group formula_171 which is called the Jacobian or the Picard group of formula_70.Two divisors formula_173 are called equivalent if they belong to the same element of formula_174, this is the case if and only if formula_169 is a principal divisor.Consider for example a hyperelliptic curve formula_176 over a field formula_2 and a point formula_25 on formula_70.