How to draw a labeled triple arrow (\Rrightarrow)

Question

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

.

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?

Answer 1

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}

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}

Answer 2

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

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

Answer 3

It is possible also to use xy package to have your symbol:

\documentclass[a4paper,12pt]{article}
\usepackage[all]{xy}
\usepackage{graphicx}

\begin{document}

Let a free text before  \raisebox{.55ex}{\xymatrix@C=3pc{ A \ar@3{->}[r]^{\txt{\tiny Small}} &B}} and after.

\xymatrix { A \ar@3{<-}[r]^{\txt{\tiny Over}} &B}

\end{document}

Explanation of the code:

1. \raisebox{.55ex}{....} to put the triple arrow approximatively to the same line of the text using graphicx package.
2. \xymatrix@C=3pc{ A \ar@3{->}[r]^{\txt{\tiny Small}} &B} it is the code of 3 line with arrow (right) or option left using <- with the over text using ^ or under using _. @C=3pc give to you the lenght of the arrow.

If you prefer to have a macro I can provide to improved my other answer.