Proposition 30
Tag 0AW6, permanent. Cite it as [Bourbaki, Tag 0AW6].
Lie Groups and Lie Algebras, chapter VI, § 1. Root systems
Assume that is irreducible. Let be an integer between 1 and and prime to . Then is an eigenvalue of of multiplicity 1.
In particular, is an exponent of , cf. Chap. V, § 6, no. 2.
We first prove a lemma:
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.