@Lénárd: thanks for pointing that out.

I’m neither a language-lawyer for English nor for C++, but what is then the purpose of http://eel.is/c++draft/temp.variadic#6:

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For the purpose of determining whether a pack satisfies a rule regarding entities other than packs, the pack is considered to be the entity that would result from an instantiation of the pattern in which it appears.

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In my understanding this means: consider the fold-expression as-if it was expanded in the current context. And that would mean, we have the question, whether an expanded fold-expression is still a fold-expression, or the expanded expression?

Cheers

Tobias