EN
Let 𝓐 and 𝓑 be mutually commuting unital C* subalgebras of 𝓑(𝓗). It is shown that 𝓐 and 𝓑 are C* independent if and only if for all natural numbers n, m, for all n-tuples A = (A₁, ..., Aₙ) of doubly commuting nonzero operators of 𝓐 and m-tuples B = (B₁, ..., Bₘ) of doubly commuting nonzero operators of 𝓑,
$Sp(A, B) = Sp(A) × Sp(B)$,
where Sp denotes the joint Taylor spectrum.