# Unwanted line breaks after equation tag when using fleqn and leqno

When you use fleqn and leqno and assign your own equations tags with \tag to equations in environments such as gather and align and you assign a tag with a certain length, then there's a line break after the tag. Given the same condition except that environment equation is used instead does not cause line breaks. How can I avoid the line breaks in the former case?

\documentclass[fleqn,leqno]{article}

\usepackage{amsmath}

\begin{document}

\begin{gather}
\tag{one}
1+1=2 \\
\tag{two}
2+2=4
\end{gather}

$$\tag{three} 1+1=2$$

\end{document}

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AFAIK, you shouldn't use both fleqn and leqno. –  egreg Nov 21 '11 at 16:47
@egreg Could you please provide a reference for why I should avoid it? Also, is there some recommended way of getting a similar result? –  N.N. Nov 21 '11 at 16:51
I see very little point in putting the number on the left of left aligned equations. Of course, if you really want to do it, you have to set \mathindent as wide as necessary in order to accommodate all your tags and leave sufficient space to avoid ambiguities. –  egreg Nov 21 '11 at 16:57

You can increase \mathindent, but I don't know why you want to use fleqn and leqno simultaneously:

\documentclass[fleqn,leqno]{article}

\usepackage{amsmath}
\setlength\mathindent{2cm}
\begin{document}

\begin{gather}
\tag{one}
1+1=2 \\
\tag{two}
2+2=4
\end{gather}

$$\tag{three} 1+1=2$$

\end{document}

-
I use fleqn and leqno because I want to flush equations to the left and also have equation numbers to the left. Is this bad practice? –  N.N. Nov 21 '11 at 16:53
@N.N. But then, the equation number could be cause some confusion as it could be taken, if it falls too close to an equation, as part of the equation. –  Gonzalo Medina Nov 21 '11 at 16:55
Why is \setlength\mathindent needed for gather but not for equation? –  N.N. Nov 22 '11 at 7:08
@N.N. perhaps you can consider opening a new question. –  Gonzalo Medina Nov 22 '11 at 11:41