Bourbaki

Proposition 1

Tag 01JH, permanent. Cite it as [Bourbaki, Tag 01JH].

Lie Groups and Lie Algebras, chapter IX, § 4. Root system associated to a compact group

— For any compact Lie group H, the Z\mathbf Z-*module* X(H)X(H) is of finite type. It is free if H is connected.

Assume first that H is connected; every element of X(H)X(H) vanishes on the derived group D(H)D(H) of H, hence we have a homomorphism X(H/D(H))⟶X(H)X(H/D(H))\longrightarrow X(H). But H/D(H)H/D(H) is connected and commutative, hence is a torus, and X(H/D(H))X(H/D(H)) is a free Z\mathbf Z-module of finite type (Spectral Theories, Chap. II, §2, no. 1, Cor. 2 of Prop. 1). In the general case, it follows from the exactness of the sequence

0⟶X(H/H0)⟶X(H)⟶X(H0), 0\longrightarrow X(H/H_0)\longrightarrow X(H)\longrightarrow X(H_0),
where X(H0)X(H_0) is free of finite type and X(H/H0)X(H/H_0) is finite, that X(H)X(H) is of finite type.

Bourbaki sets the proof directly after the statement, and the corpus does not separate them, so what is above is the statement and its proof together.

Cited by

Nothing.

Cites

  • *Spectral Theories*, Chap. II, §2, no. 1, Cor. 2 of Prop. 1 not in this corpus: TS II
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