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I am trying to say that a single-valued function satisfies the definition of a multi-valued function. For example, if I define the following: $$\newcommand{\Log}{\operatorname{Log}} f(z):=\Log(z)+2\lfloor{|z|}\rfloor\pi i$$ I want to say $f(z)$ is an instance of $\log(z)$ in the sense that $e^{f(z)}=z$.

Are there any symbols or phrases to present this idea? If I just say “$f(z)=\log(z)$”, it would be ambiguous. If I say “$f(z)\in\log(z)$”, that would mean $\log(z)$ is a set. If I say “$f(z)$ is an instance of $\log(z)$”, it will be quite confusing. I can say “$e^{f(z)}=z$” for this example. However, in case I had to define a multi-valued function in a complicated way, I would not want to repeat the definition of that multi-valued function many times.

How to present the idea that “(a single-valued function) is an instance of (a multi-valued function)” in a clear, unambiguous manner?

Tyrell
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    A suggestion: add [tag:terminology] to your tags. – José Carlos Santos Jan 08 '25 at 12:22
  • It would help to explain why this is something you want to do, since simply saying this in ordinary natural language is almost certainly going to be far more reader-friendly than lots of symbolic expressions that have to be deciphered, which greatly increases the possibility of both error and misinterpretation on the part of the writer and the reader. That said, sometimes putting things in highly symbolic form can be helpful (e.g. see the earlier parts of this answer), so if you are in such a situation, then it would help to explain it. – Dave L. Renfro Jan 08 '25 at 13:24
  • @DaveL.Renfro I wanted to do this because I defined a multi-valued function using three lines of conditions, and I struggled to explain my thoughts. I am afraid that my English is not good enough to clearly present my ideas. Also, natural languages inevitably have some degree of ambiguity, I hope I can make the concept of “instance of multi-valued function” as clear as possible. – Tyrell Jan 08 '25 at 16:30
  • If it helps, I'm used to multi-valued functions being formulated as set-valued functions, so if using this for your "parent conceptual framework", single-valued functions can be identified as those whose outputs are singleton sets. I don't know if this helps any. Regarding "my English is not good enough to clearly present my ideas", your English is quite good from what I can tell. – Dave L. Renfro Jan 08 '25 at 16:58

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