 Examples of such fields are function fields (or power series fields) of one variable over perfect base fields.Over F2, the Arf invariant is 0 if the quadratic form is equivalent to a direct sum of copies of the binary form formula_22, and it is 1 if the form is a direct sum of formula_23 with a number of copies of formula_22.William Browder has called the Arf invariant the "democratic invariant" because it is the value which is assumed most often by the quadratic form.