6

There exists the ams-symbol \Rrightarrow which gives a triple arrow like

triple arrow.

Now I want to endow the arrow with a label, which for example in the case of double arrows works with \xRightarrow{f}. But unfortunately the corresponding command for labeled triple arrows \xRrightarrow seems not to exist.

I am aware of the \overset command, but overset doesn't lengthen the arrow in case the label is longer than the \xRrightarrow symbol.

So my question is: What is the simplest way to draw a labeled triple arrow whose length is adjusted to the length of its label?

  • 2
    in order to extend an arrow, there must be an extender. for the computer modern fonts, the extender for (horizontal) two-stem arrows is the equals sign. there wasn't any extender made specifically for three-stem arrows, although i suppose that the \equiv symbol could be tried. the technique should be derivable from the definition of \Longrightarrow in amsmath.sty, but i haven't got time to try it right now. – barbara beeton May 9 '18 at 21:45
11

You're lucky: \equiv and \Rrightarrow can be combined.

\documentclass{article}
\usepackage{amsmath,amssymb}

\makeatletter
\newcommand{\xRrightarrow}[2][]{\ext@arrow 0359\Rrightarrowfill@{#1}{#2}}
\newcommand{\Rrightarrowfill@}{\arrowfill@\equiv\equiv\Rrightarrow}
\newcommand{\xLleftarrow}[2][]{\ext@arrow 3095\Lleftarrowfill@{#1}{#2}}
\newcommand{\Lleftarrowfill@}{\arrowfill@\Lleftarrow\equiv\equiv}
\makeatother

\begin{document}

$A\xRrightarrow{fghi}B$

$A\xLleftarrow{fghi}B$

\end{document}

enter image description here

One can also add the symmetric version:

\documentclass{article}
\usepackage{amsmath,amssymb}

\makeatletter
\newcommand{\xRrightarrow}[2][]{\ext@arrow 0359\Rrightarrowfill@{#1}{#2}}
\newcommand{\Rrightarrowfill@}{\arrowfill@\equiv\equiv\Rrightarrow}
\newcommand{\xLleftarrow}[2][]{\ext@arrow 3095\Lleftarrowfill@{#1}{#2}}
\newcommand{\Lleftarrowfill@}{\arrowfill@\Lleftarrow\equiv\equiv}
\newcommand{\xLleftRrightarrow}[2][]{\ext@arrow 3399\LleftRrightarrowfill@{#1}{#2}}
\newcommand{\LleftRrightarrowfill@}{\arrowfill@\Lleftarrow\equiv\Rrightarrow}
\makeatother

\begin{document}

$A\xRrightarrow{fghi}B$

$A\xLleftarrow{fghi}B$

$A\xLleftRrightarrow{fghi}B$

\end{document}

enter image description here

  • I have not undestood the question, then. :-( As usual for me. – Sebastiano May 10 '18 at 19:55
3

Label over \Rrightarrow and \rightrightarrows. It is possible to use a triple arrows with TikZ macro: see this link Custom arrow shaft in tikz.

enter image description here

\documentclass[a4paper,12pt]{article}
\usepackage{amssymb, amsmath}
\begin{document}
\[a \stackrel{\text{label}}{\Rrightarrow}
 f\]
 \[a \stackrel{\text{label}}{\rightrightarrows}
 f\]
\end{document}

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