Let 
be a 
-algebra,
then an element 
is called a partial isometry if 
.
Partial Isometry Element
This entry contributed by Mohammad Sal Moslehian
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References
Murphy, G. J.
-Algebras and Operator Theory. New York: Academic
Press, 1990.Referenced on Wolfram|Alpha
Partial Isometry ElementCite this as:
Weisstein, Eric W., with contributions by Mohammad Sal Moslehian. "Partial Isometry Element." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/PartialIsometryElement.html