# (Total and Surjective) Relation - arrows

I am looking for following symbols:

Total Relation: <<->
Surjective Relation: <->>
Total surjective Relation: <<->>

This is the sort of thing I’m looking for (source):

Can anybody help me?

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Can you point to some source showing the symbols you're after? –  egreg Feb 4 '14 at 10:29
handbook.event-b.org/current/files/EventB-Summary.pdf Relations (5.4 - 5.6) –  Philip Errichte-Es Feb 4 '14 at 10:35
Welcome to TeX.SX! You can have a look at our starter guide to familiarize yourself further with our format. You should start by seeing whether tex.stackexchange.com/q/14/15925 leads you to the correct symbols. –  Andrew Swann Feb 4 '14 at 10:37
I guess that they are using a trick, a kind of two arrows with negative space. –  Sigur Feb 4 '14 at 10:39
@egreg, the arrow tips from amssymb does not match with the default arrow tips (compare $S\mathrel{\parbox[b]{0pt}{$\twoheadleftarrow$}\rightarrow }T$). –  Sigur Feb 4 '14 at 10:50

Here's a way to build symbols like in the document you link to:

\documentclass{article}
\usepackage{mathtools}

\newcommand{\negjoinrel}{\mathrel{\mkern3mu}}
\newcommand{\rlaprel}[1]{\mathrel{\mathrlap{#1}}}
\newcommand{\rel}{\rlaprel{\leftarrow}\negjoinrel\rightarrow}
\newcommand{\trel}{\rlaprel{\leftarrow}\negjoinrel\rlaprel{\leftarrow}\rightarrow}
\newcommand{\srel}{\rlaprel{\leftarrow}\rlaprel{\rightarrow}\negjoinrel\rightarrow}
\newcommand{\tsrel}{\rlaprel{\leftarrow}\negjoinrel\rlaprel{\leftarrow}
\joinrel\rlaprel{\rightarrow}\negjoinrel\rightarrow}

\begin{document}
\noindent
$A\rel B\trel C\srel D\tsrel E$

\noindent$\rel$\\$\trel$\\$\srel$\\$\tsrel$
\end{document}


You can see that they all have the same width.

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Thank you very much. Exactly what I was searching for. –  Philip Errichte-Es Feb 4 '14 at 12:02

Is this what you want?

$\ll \gg$


Or this (from amssymb):

$\twoheadleftarrow \twoheadrightarrow \rightarrowtail \leftarrowtail$


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The second examples (\twoheadleftarrow,...) needs an > on the right side. –  Philip Errichte-Es Feb 4 '14 at 10:33
–  Sigur Feb 4 '14 at 10:36