# Excluding lines starting with certain objects from indentation

Is there a way to exlude certain lines from indentation ? For example, I'd like to have every line that starts with a certain object, like the \Longrightarrow in the following MWE, to not be indented. Is there a way to do this without adding \noindent at the start of every such line ?

The command should be robust so as to also permit other identifier of such lines than mathematical symbols: More concretely it should be possible to have the option to also indent lines consisting of a sole LaTeX command (like \textcyr{\char143}) lines starting with a \fbox.

I'd be grateful for every tip!!

\documentclass[12pt,a4paper]{article}
\usepackage[latin1]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\begin{document}

The indentation is visible in this line, as one can see by type a lot of text text text text text text text text text text text text text text text ...

$\Longrightarrow$ Because I used the arrow at the start, this line should *never* be intended.

Now indentation is active again...

\end{document}

• The Longrightarrow is tricky as you are already in math mode. But other macros that are not in math mode can be redefined as \let\OlfFbox\fbox and \def\fbox{\noindent\OlfFbox}. Then using \fbox will automatically not be indented. If you are willing to use \Longrightarrow instead of $\Longrightarrow$, then you can use \let\OldLongrightarrow\Longrightarrow and \def\Longrightarrow{\noindent\ensuremath{\OldLongrightarrow}}. – Peter Grill Dec 12 '14 at 18:14
• Actually this comment was, what I was really looking for, since I already have several lines that are to be intendet and don't want to change the command of each line to some new command that I define to not be indented, but rather redefine the command (but the answerer couldn't know that of course, since I wasn't precise about this point). – l7ll7 Dec 13 '14 at 17:07

You have to avoid starting math mode, or it would be too late for removing the indentation:

\documentclass[12pt,a4paper]{article}

\newcommand{\niLongrightarrow}{%
\noindent\ensuremath{\Longrightarrow}%
}

\begin{document}

The indentation is visible in this line, as one can see by type a lot of text text text
text text text text text text text text text text text text ...

\niLongrightarrow{} Because I used the arrow at the start, this line should *never* be
intended.

Now indentation is active again and $a\niLongrightarrow b$...

\end{document}


But using \noindent is simpler.

• Is there any drawback to redefining the original as \let\svLRA\Longrightarrow\def\Longrightarrow{\noindent\ensuremath{\svLRA}}, in case the OP wanted to not introduce a new macro name? – Steven B. Segletes Dec 13 '14 at 0:54
• @StevenB.Segletes Yes, there are: the symbol is not used in its mathematical meaning, in this case, but just as a graphic device. I used \ensuremath for convenience, but \ensureNONmath would be better. – egreg Dec 13 '14 at 10:29