In the *Grundgesetze der Arithmetik*, Frege used a number of strange characters for notation. I would be most interested to know anything about the *typography* (origin, usage and so on) of the strange U with a flourish which occurs in the following.

I am no logician, but I am given to understand that the symbol (U in the following) is used as "a function-name ‘Ux’ in such a way that if y is the extension of a relation, then Uy is the extension of its inverse".

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Thanks in advance!

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In response to some of the comments as to the relevance of this question to mathematics, I add my motivation for it. I have heard it said (by a rather famous Frege scholar) that Frege chose his notation by taking whatever was available in the [type] box. I have come to the view that this is not the case, and that Frege often chose his notation rather carefully. This rather obscure issue leads me to seek the typographic origins of these symbols. I know the origins of most of those in the *Grundgesetze* (which are surprisingly diverse: phonetics, commerce, German, Greek, ...) but a few remain unidentified, hence the question.

Uis a natural choice. $\endgroup$justabout the sign, but also about what is being signified. If it were a fancy $U$ and Frege meant it to signify 'Umkehrung', that would be one thing. If it were a rotated $A$, and carried other resonances for Frege, that would be another. $\endgroup$aminterested in fonts and typography, too. Yet, in particular in view of your motivation, it just seems better/more efficient to me to ask this elsewhere (for example the site mentioned by Yuji Tachikawa). As your question really seems to be 'what is this typographic symbol?' So, I'd ask experts on typographic symbols, as opposed to mathematicians/logicians that are experts on the meaning of this symbol as used Frege. (Hope this makes sense.) $\endgroup$4more comments