I was looking through some examples which applied the duality principle while studying for an up and coming exam when it hit me that the transform applied 4 times gives you back the same function.(adsbygoogle = window.adsbygoogle || []).push({});

So is there some theory that uses this? perhaps some sort of operator?

I thought it interesting but couldn't find any information on it, what should I look up to learn more about this?

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# Four-fold periodicity of Fourier transform

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