Type: Article
Publication Date: 1967-01-01
Citations: 22
DOI: https://doi.org/10.1090/s0002-9939-1967-0217060-4
PROOF. (1) -*(3): We suppose K((X)) =L and we consider a sequence { a, } % of nonzero elements of D. For any nonnegative integer k, we define c,c = (aoa1 ... ak)-1. Then c = _=0 CkXkGK[[X]]CL, so that there is a nonzero element b = EUo bkXk of D [[X]] such that bczD [[X]]. If the power series b has order r, then b/Xr (ED [ [X] ] and (b/Xr)cED [ [X] ], so we may assume that rO -that is, bo-00. Then if m is a nonnegative integer, the coefficient of Xm in bc is