Lemma 2
Tag 09V7, permanent. Cite it as [Bourbaki, Tag 09V7].
Lie Groups and Lie Algebras, chapter I, § 2. Enveloping algebra of a Lie algebra
There exists an -mapping of into such that:
(1) for ; (2) (mod. ) if has elements.
By Lemma 1 there exists a homomorphism of the K-module into satisfying, for all , conditions (A), (B), (C) (where is replaced by ). This homomorphism defines a homomorphism of the K-module into the K-module and is an -mapping because of condition (C). Finally, satisfies properties (1) and (2) of the lemma because of conditions (A) and (B).
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.