An involutive Banach algebra is a Banach algebra 
which is an involutive algebra and 
for all 
.
Involutive Banach Algebra
This entry contributed by Mohammad Sal Moslehian
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References
Bonsall, F. F. and Duncan, J. Complete Normed Algebras. New York: Springer-Verlag, 1973.Referenced on Wolfram|Alpha
Involutive Banach AlgebraCite this as:
Weisstein, Eric W., with contributions by Mohammad Sal Moslehian. "Involutive Banach Algebra." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/InvolutiveBanachAlgebra.html