Let A be a commutative complex Banach algebra with an identity e with ||e|| = 1. In 1968, A. M. Gleason [4], J. P. Kahane and W. Zelazko [8] proved that, φ ∈ A~* is multiplicative if and only if φ(x) ∈ σ(x) for all x ∈ A, this is called the GKZ theorem.
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机译：设A为具有|| e ||的标识e的可交换复Banach代数。 =1。1968年，AM Gleason [4]，JP Kahane和W. Zelazko [8]证明，当且仅当对所有x∈A而言，φ∈A〜*是可乘的，这称为GKZ定理。
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