I'm reading QFT: Basics in Mathematics and Physics, by Eberhard Zeidler. Once in a while, in his proofs, I see the word (abbreviation?) Ad. For instance on page 375. The author is German and I suppose this imight be common practice in German texts. Does anyone here know what it means?(adsbygoogle = window.adsbygoogle || []).push({});

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# What is Ad in a proof?

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