# Equivalence arrow in LaTeX

I have an equation like

\documentclass[12pt,a4paper]{report}
\usepackage[latin1]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsthm}
\begin{document}
\begin{align*}
a+b+c+d+e+f&=g\\
\Leftrightarrow a &=g-a-b-c-d-e-f
\end{align*}
\end{document}


I'd like to have the arrow left to both equation, how do I do this?

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Welcome to TeX.SX! Please make your code compilable (if possible), or at least complete it with \documentclass{...}, the required \usepackage's, \begin{document}, and \end{document}. That may seem tedious to you, but think of the extra work it represents for TeX.SX users willing to give you a hand. Help them help you: remove that one hurdle between you and a solution to your problem. –  Jubobs May 9 at 19:42

Do you mean like this?

\documentclass{article}
\usepackage{amsmath}

\begin{document}
\begin{alignat*}{2}
&\iff & a+b+c+d+e+f &=g             \\
&\iff &           a &=g-b-c-d-e-f
\end{alignat*}
\end{document}

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Yes, thank you very much! –  user51412 May 9 at 19:50
@user51412 Accepting and upvoting answers is the preferred way here to say “thank you” to users who helped you :) –  Jubobs May 9 at 19:52
I think you should clarify the reason why you used \iff{} instead of \iff: not only because here it's useful, but also because \iff{} in other places might give you “problematic” spacing. E.g., I've seen people using \dots{} in math. –  Manuel May 9 at 20:17
@Manuel Actually, {} doesn't seem to be useful in this case, so I just removed it. –  Jubobs May 9 at 21:07
@Jubobs Yes, it's useful. You still see a space because \iff ensures there is some space around it… but there “should” be a {} there. Just imagine it's a \to instead of \iff in that case the difference is easier to spot since if you don't use {} you end up with no space. –  Manuel May 9 at 23:14

## Notes:

• As this is just a single equation, you don't really need to use align, but in case you have other equations in your actual use case I left it as align:

## Code:

\documentclass{article}

\usepackage{amsmath}

\begin{document}
If you mean to say "if, and only if" you should use \verb|\iff|:
\begin{align*}
a+b+c+d+e+f&=g \iff a =g-a-b-v-d-e-f
\end{align*}

\end{document}

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