The Carl Neumann criterion states that if 
is a unital Banach algebra, 
, and 
, then 
can be represented by the series 
. It is therefore a criterion for the
invertibility of 
.
Carl Neumann Criterion
This entry contributed by Mohammad Sal Moslehian
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References
Murphy, G. J. C*-Algebras and Operator Theory. New York: Academic Press, 1990.Referenced on Wolfram|Alpha
Carl Neumann CriterionCite this as:
Weisstein, Eric W., with contributions by Mohammad Sal Moslehian. "Carl Neumann Criterion." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/CarlNeumannCriterion.html