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Josueknorst (talk  contribs) m (→Examples) 

for all <math>x</math> and <math>y</math> in <math>H_1</math>, where the horizontal bar represents the [[complex conjugate]]. If additionally one has <math>H_1 = H_2</math> then U is called an '''antiunitary operator'''.
Antiunitary operators are important in quantum theory because they are used to represent certain symmetries, such as [[Tsymmetry#Time reversal in quantum mechanicstime
==Invariance transformations==
