“…Since I is projective, there exists an i d e m p o t e n t n × n m a t r i x M with elements in R such t h a t U M -= U a n d U ± -: a n n M. Since R is an I D ring, it follows f r o m [6] B y Proposition 1.5, I is g e n e r a t e d b y U P . L e t n be the smallest n u m b e r of generators t h a t are required to generate I, a n d let 1 be g e n e r a t e d b y U -(a 1, a~ .…”