Corollary 1

Tag 0ATS, permanent. Cite it as [Bourbaki, Tag 0ATS].

Lie Groups and Lie Algebras, chapter V, § 6. The Coxeter transformation

If $(m_i)_{1 \leq i \leq l}$ is the increasing sequence of exponents of W, the order of W is equal to $(m_1 + 1)(m_2 + 1) \ldots (m_l + 1)$ .

This follows from the relations $m_j + 1 = p_j$ and § 5, Cor. of Th. 3.

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

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