Bourbaki

Example 1

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

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

If G is semi-simple of rank 1, then D∗(G,T)D^*(G,T) and D∗(G,T)D_*(G,T) are necessarily isomorphic to one of the two diagrams Δ2=(Z,0,{2,−2})\Delta_2= (\mathbf{Z},0,\{2,-2\}), Δ1=(Z,0,{1,−1})\Delta_1= (\mathbf{Z},0,\{1,-1\}). If G is isomorphic to SU(2,C),D∗(G,T)\mathbf{S}\mathbf{U}(2,\mathbf{C}), D_*(G,T) is isomorphic to Δ1\Delta_1 (since G is simply-connected) so D∗(G,T)D^*(G,T) is isomorphic to Δ2\Delta_2. If G is isomorphic to SO(3,R),D∗(G,T)\mathbf{S}\mathbf{O}(3,\mathbf{R}), D^*(G,T) is isomorphic to Δ1\Delta_1 (since C(G)={1}C(G) =\{1\}), so D∗(G,T)D_*(G,T) is isomorphic to Δ2\Delta_2.

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

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Cites

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Transcribed from the printed volume. Not translated.