Remark 3
Tag 0ANZ, permanent. Cite it as [Bourbaki, Tag 0ANZ].
Lie Groups and Lie Algebras, chapter IV, § 2. Tits Systems
Assumption (3) is implied by the following condition:
(3') U is generated by the commutators b^{-1} u^{-1} b u with u \in U and b \in B \cap G_1.
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.
Cited by
Nothing.
Cites
Nothing.