2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/58533An improved (streamlined and extended) version of this paper is available as math.RA/0203010, which however omits some details. We recommend the later version unless details are essential.Theorems 1 and 3 corrected (theta replaced by its inverse)Rings and AlgebrasHigh Energy Physics - TheoryMathematical Physicstext