Suppose that G is finite-dimensional. Let (e1,…,en) be a basis of L(G), (e1∗,…,en∗) the dual basis, (cijk) the constants of structure of L(G) relative to the basis (e1,…,en) and ωi (resp. ωi′) the left (resp. right) invariant differential form on G with values in K such that (ωi)e=ei∗ (resp. (ωi′)e=ei∗). Then
dωk+i<j∑cijkωi∧ωj=0(k=1,2,…,n) dωk′−i<j∑cijkωi′∧ωj′=0(k=1,2,…,n). If
r<s,
(dωk)e(er,es)=−(ωk)e([er,es])=−i∑crsi(ωk)e(ei)=−crsk=−i<j∑cijk(ωi∧ωj)e(er,es). The argument is similar for the
ωk′.
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.
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