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TL:DR; I suggest to remove deprecated tags that still exist on some questions, in order to prevent them from being added to new questions.
There are a few tags which are deprecated and should not be used at all, but still exist on the site.1 Ideally such tags should be completely removed, but th...
We start with $ZF$.
The axiom of countable choice, $AC_\omega$, says that any set product of nonempty sets with a countable index set is nonempty. For any $ZF$-definable set $A$, we should be able to define $AC_A$ in an analogous manner: any product of nonempty sets with index set $A$ is nonemp...1
In mathematics, an exponential sum may be a finite Fourier series (i.e. a trigonometric polynomial), or other finite sum formed using the exponential function, usually expressed by means of the function
e
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x
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=
exp
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2
π
i
x
)
.
{\displaystyle e(x)=\exp(2\pi ix).\,}
Therefore, a typical exponential sum may take the form
∑
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e
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