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I see different documents using $\cdot$ or $\star$ to depict multiplication.

For e.g. some use $4.5.6 = 120$ while others may be use $4\star 5\star 6 = 120$.

And in case it involves brackets, I also see stuff like

$e(x) = f(x)g(x)h(x)$

or

$e(x) = f(x)\cdot g(x) \cdot h(x)$

or

$e(x) = f(x)\star g(x) \star h(x)$

Are there any rules?

user93353
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    I don't think there are any rules regarding this no, unless of course one of the symbols is already used for something else ($*$ or $\star$ for a convolution, $\cdot$ for a dot product), in which case one would try to avoid using the same symbol for two different things. – Bruno B Aug 14 '23 at 09:06
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    $\star$ is less common than $\times$. Anything you use can get overloaded ($\cdot$ and $\times$ mean different things when multiplying vectors) so your aim when using any symbol or non should be clarity in the particular context. There is always the risk of confusion: does $8.5= \frac{17}{2}$ or $40$? Does $8\frac12$ mean $\frac{17}{2}$ or $4$? – Henry Aug 14 '23 at 09:25

1 Answers1

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There are (as is the case with so many notation-related questions) no hard rules, though, as Bruno B. pointed out it's always good practice to not re-use symbols. Personally I think most mathematicians will prefer $\cdot$ (\cdot in LaTeX), and in the case of the function applications I think leaving the symbol completely is fine too.

WalrusGumboot
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