Let G be a Lie group and π1,…,πn analytic linear representations of G on finite-dimensional vector spaces E1,…,En. Then the representation π1⊗⋯⊗πn of G (Appendix) is analytic and L(π1⊗⋯⊗πn) is the tensor product of L(π1),…,L(πn).
The mapping (A1,…,An)↦A1⊗⋯⊗An of L(E1)×⋯×L(En) into L(E1⊗⋯⊗En) is multilinear, whence the fact that π is analytic. Consider the mapping (x1,…,xn)↦x1⊗⋯⊗xn of E1×⋯×En into
E1⊗⋯⊗En. By Proposition 41, we see that
(L(π)a)(x1⊗⋯⊗xn)=i=1∑nx1⊗⋯⊗(L(πi)a)xi⊗⋯⊗xn for all
a∈L(G),
xi∈Ei for
1≤i≤n. Hence
L(π) is the tensor product of the
L(πi).
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.