Bourbaki

Proposition 8

Tag 09WA, permanent. Cite it as [Bourbaki, Tag 09WA].

Lie Groups and Lie Algebras, chapter I, § 3. Representations

Let gg be a Lie algebra and MM a gg-module. Suppose that MM, considered as a KK-module, admits a finite basis. The bilinear form associated with MM is invariant.

For x,y,zx, y, z in gg, we have:

Tr⁡([x,y]MzM)=Tr⁡(xMyMzM)−Tr⁡(yMxMzM)=Tr⁡(xMyMzM)−Tr⁡(xMzMyM)=Tr⁡(xM[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*}

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

Cited by

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Cites

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Transcribed from the printed volume. Not translated.