Library / Lie Groups and Lie Algebras / Chapter I / § 3
Proposition 8
Tag 09WA, permanent. Cite it as [Bourbaki, Tag 09WA].
Lie Groups and Lie Algebras, chapter I, § 3. Representations
Let g g g be a Lie algebra and M M M a g g g -module. Suppose that M M M , considered as a K K K -module, admits a finite basis. The bilinear form associated with M M M is invariant.
For x , y , z x, y, z x , y , z in g g g , we have:
Tr ( [ x , y ] M z M ) = Tr ( x M y M z M ) − Tr ( y M x M z M ) = Tr ( x M y M z M ) − Tr ( x M z M y M ) = Tr ( x M [ y , z ] M ) .
\begin{align*}
\operatorname{Tr}([x, y]_M z_M) &= \operatorname{Tr}(x_M y_M z_M) - \operatorname{Tr}(y_M x_M z_M) = \operatorname{Tr}(x_M y_M z_M) - \operatorname{Tr}(x_M z_M y_M) \\
&= \operatorname{Tr}(x_M [y, z]_M).
\end{align*}
Tr ([ x , y ] M z M ) = Tr ( x M y M z M ) − Tr ( y M x M z M ) = Tr ( x M y M z M ) − Tr ( x M z M y M ) = Tr ( x M [ y , z ] M ) .
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.
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Transcribed from the printed volume. Not translated.