Why doesn't lineno number a paragraph when it is followed by an indented equation?

While searching for the source of missing line numbers, I realized that paragraphs followed immediately by an equation have no line number, but this is fixed when a space is included,

e.g. the following document has no line numbers:

\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{lineno}
\linenumbers
\begin{document}
Lorem ipsum dolor sit amet, consectetur adipiscing elit:
$$1+1=2$$
\end{document}


But this one does:

\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{lineno}
\linenumbers
\begin{document}
Lorem ipsum dolor sit amet, consectetur adipiscing elit:

$$1+1=2$$
\end{document}


The only difference is the space above the equation.

• Why is this the case (and is there a simple workaround)?

• Is it incorrect to include an indented equation in a paragraph, or is this just a 'feature' of lineno?

-

$$...$$ is obsolete, see Why is [ … ] preferable to . If you use the correct LaTeX displayed math environment, the numbering works without the empty line:

\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{lineno}
\linenumbers
\begin{document}
Lorem ipsum dolor sit amet, consectetur adipiscing elit:
$1+1=2$
\end{document}


-
thank you, is $ also obsolete? – David Aug 15 '11 at 21:04 @David: that's true, see: Are $$and$$ preferable to$. At least: $$...$$ is LaTeX syntax, so better supported in LaTeX. $...$ is plain TeX. However, usually both work well, many prefer $...$ because it's easier to write or just classic. –  Stefan Kottwitz Aug 15 '11 at 21:09
@David: $$ and $$ are fragile by default. So, as Will Robertson said, don't use them unless you use fixltx2e package. And the default $$ and $$ have very few advantages compared with \$. –  Leo Liu Aug 16 '11 at 5:05
@StefanKottwitz, what could I do if I need numbered equations? –  Sigur Apr 3 '13 at 20:08
@Sigur Use an equation environment. –  Stefan Kottwitz Apr 3 '13 at 20:37
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