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I want to work with fractions, quantifying a fraction as single element, but \forall and \exists are being displayed too small near \dfrac. And mathlarger doesn't seem to work.

I know only the basics of latex and haven't found anything that resolves this problem.

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{relsize}

\begin{document}
    \begin{enumerate}
        \item Neutral: $\mathlarger{\exists!} \dfrac{x}{y} : \dfrac{x}{y} + \dfrac{c}{d} = \dfrac{c}{d}$
    \end{enumerate}
\end{document}
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  • 1
    What about 2\cdot\dfrac{1}{3}? Would you think that the 2 is too small?
    – egreg
    Commented Oct 24, 2022 at 9:04
  • No, the number 2 is not small, 1 and 3 are natural numbers and so 2, it makes sense all have the same size. But the quantifier seems to me that he should have the same size of what follows. Commented Oct 24, 2022 at 9:09
  • 1
    I see no reason to. By the way, what would \exists \frac{x}{y} mean?
    – egreg
    Commented Oct 24, 2022 at 9:10
  • 1
    Have you seen any published math texts that expand quantifiers in that way? As egreg hints they are usually set as normal characters in the current font size Commented Oct 24, 2022 at 9:11
  • 2
    Let me suggest another solution: Replace the quantifier by “There exists...”. Quantifiers and implication arrows don’t really add any benefit to the text. Too much notation just makes the text unnecessarily heavy for the reader.
    – Gaussler
    Commented Oct 24, 2022 at 9:15

1 Answer 1

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Perhaps what you need is a symbol which acts like a large operator. See the following codes and output.

\documentclass{article}
\usepackage{amsmath}
\usepackage{scalerel}
\makeatletter
\DeclareMathOperator*{\bigexistsone}{\scalerel*{\exists!}{\sum}}
\makeatother

\begin{document}
\begin{enumerate}
\item The original one in text style in lines: $\exists!\dfrac{x}{y}\left(\dfrac{x}{y} + \dfrac{c}{d} = \dfrac{c}{d}\right)$, and the new one in display style between lines: $$\exists!\dfrac{x}{y}\left(\dfrac{x}{y} + \dfrac{c}{d} = \dfrac{c}{d}\right).$$
\item The new one in text style in lines: $\bigexistsone\dfrac{x}{y}\left(\dfrac{x}{y} + \dfrac{c}{d} = \dfrac{c}{d}\right)$, and the new one in display style between lines: $$\bigexistsone\dfrac{x}{y} \left(\dfrac{x}{y} + \dfrac{c}{d} = \dfrac{c}{d}\right).$$
\end{enumerate}

\end{document}

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