We express the discriminant of the polynomial relations of the fusion ring,
in any conformal field theory, as the product of the rows of the modular matrix
to the power -2. The discriminant is shown to be an integer, always, which is a
product of primes which divide the level. Detailed formulas for the
discriminant are given for all WZW conformal field theories.Comment: 19 pages, one table. Minor typos correcte
