Bourbaki

Corollary 3

Tag 04IC, permanent. Cite it as [Bourbaki, Tag 04IC].

Commutative Algebra, chapter III, § 4. Lifting in complete rings

*With the notation & Corollary 2, let a∈Ana \in \mathbf{A}^n; let us write e=Jr(n−r)(a)e = J_r^{(n-r)}(\mathbf{a}) (not necessarily invertible in A\mathbf{A}) and suppose that f(a)≡0f(\mathbf{a}) \equiv 0 (mod. e2m×(n−r)e^{2m^{\times(n-r)}}). Then there exist n−rn - r formal power series without constant term ϕi\phi_i (r+1≤i≤nr + 1 \leq i \leq n) in A[[X1,…,Xr]]\mathbf{A}[[X_1, \ldots, X_r]] such that, for all t=(t1,…,tr)∈m×rt = (t_1, \ldots, t_r) \in m^{\times r},

fi(a1+e2t1,…,ar+e2tr,ar+1+eϕr+1(t),…,an+eϕn(t))=0 f_i(a_1 + e^2 t_1, \ldots, a_r + e^2 t_r, a_{r+1} + e \phi_{r+1}(t), \ldots, a_n + e \phi_n(t)) = 0

for r+1≤i≤nr + 1 \leq i \leq n.

*For 1≤i≤r1 \leq i \leq r, let fi(X)=Xi−af_i(X) = X_i - a, and let u=(f1,…,fn)u = (f_1, \ldots, f_n); then Ju(a)=eJ_u(a) = e and Theorem 2 may be applied to the system uu. With the notation of Theorem 2 it follows from the above definitions that gi(X)=Xg_i(X) = X, for 1≤i≤r1 \leq i \leq r, whence hi(X)=Xih_i(X) = X_i for 1≤i≤r1 \leq i \leq r; moreover, if M′∈Mn(A)M' \in \mathbf{M}_n(\mathbf{A}) is such that Mu(a).M′=eInM_u(a) . M' = e I_n, M′M' is of the form

(eIr0∗∗). \begin{pmatrix} e I_r & 0 \\ * & * \end{pmatrix}.

Replacing yy by M′.zM'.z (where z=(z1,…,zn)∈m×nz = (z_1, \ldots, z_n) \in m^{\times n}) in formula (20), we obtain

fi(a1+e2z1,…,ar+e2zr,ar+1+ehr+1(M′.z),…,an+ehn(M′.z))=&(a)+e2zifor 1≤i≤n. f_i(a_1 + e^2 z_1, \ldots, a_r + e^2 z_r, a_{r+1} + e h_{r+1}(M'.z), \ldots, a_n + e h_n(M'.z)) = \& (a) + e^2 z_i \quad \text{for } 1 \leq i \leq n.

By hypothesis, fj(a)=e2bjf_j(a) = e^2 b_j, where bj∈mb_j \in m for r+1≤j≤nr + 1 \leq j \leq n. Let us write ψj(X1,…,Xr)=hj(M′.X)\psi_j(X_1, \ldots, X_r) = h_j(M'.X) and

ϕj(X1,…,Xr)=ψj(X1,…,Xr,−br+1,…,−bn) \phi_j(X_1, \ldots, X_r) = \psi_j(X_1, \ldots, X_r, -b_{r+1}, \ldots, -b_n)

for r+1≤j≤nr + 1 \leq j \leq n. For r+1≤i≤nr + 1 \leq i \leq n, substituting tjt_j for zjz_j for 1≤j≤r1 \leq j \leq r and bjb_j for zjz_j for r+1≤j≤nr + 1 \leq j \leq n in (26), we obtain relations (25) for all t∈m×rt \in m^{\times r}.

Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.

Cited by

Nothing.

Cites

Transcribed from the printed volume. Not translated.