2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/73238Let k be a perfect field of positive characteristic, k(t)_{per} the perfect closure of k(t) and A=k[[X_1,...,X_n]]. We show that for any maximal ideal N of A'=k(t)_{per}\otimes_k A, the elements in \hat{A'_N} which are annihilated by the "Taylor" Hasse-Schmidt derivations with respect to the X_i form a coefficient field of \hat{A'_N}.Final versionCommutative Algebra13F25, 13N15, 13B35, 13A35text