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I would like to have a superscript symbol attached to the implies-arrow, i.e., something like that

\[ \implies^f \]

However, this does not work. A similar question was asked here: question

But just for a text above the arrow. So this does not solve my problem. Does someone has an idea how to solve this? I would like to have the same arrow length as the AMSMath implies arrow has.

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Max Maier
  • 859

1 Answers1

5

The definition of \implies is

% amsmath.sty, line 308:
\newcommand{\implies}{\DOTSB\;\Longrightarrow\;}

which means that you're setting the superscript after the thick space.

My suggestion is to define a new command

\documentclass{article}
\usepackage{amsmath}

\newcommand{\simplies}{\DOTSB\Longrightarrow}

\begin{document}

\begin{align*}
& a \simplies^f b \\
& a \implies b \\
& a \implies^f b
\end{align*}

\end{document}

The spacing around \implies is too big anyway. The second and third line are just for comparison.

enter image description here

If you want to preserve the spacing of \implies, you have no choice other than defining \simplies with an argument; probably optional, so you can use \simplies as a drop-in replacement for \implies:

\newcommand{\simplies}[1][]{\DOTSB\;\implies^{#1}\;}

and the above formula should be typed as

a \simplies[f] b
egreg
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