In chapter IV, paragraph 2 of Neukirch's Class Field Theory he writes

The adeles form a ring, denoted by $$\mathbb{A}_K = \prod_\mathfrak{p} K_\mathfrak{p}$$ where addition and multiplication is defined componentwise.

Except, he doesn't write $\prod$ but something like this picture, i.e. a product sign with a bar underneath it. I can't figure out what he means by this.

Edit: Detexify tells me that the symbol is \Gemini in $\LaTeX$, which might help someone. Personally, if I had to guess it seems to be related to taking only elements with finitely many non-trivial factors.


I have found him using the same symbol in other books (Algebraic Number Theory) where he explains the use as the restricted direct product.


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