  For each natural number $n$, we define a category whose objects are
discriminant algebras in rank $n$, i.e. functorial means of attaching to each
rank-$n$ algebra a quadratic algebra with the same discriminant. We show that
the discriminant algebras defined in [2], [6], and [10] are all isomorphic in
this category, and prove furthermore that in ranks $n \leq 3$ discriminant
algebras are unique up to unique isomorphism.
