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<html>
<head><title>Help On LaTeX Modes</title></head>
<body bgcolor="#ffffff" text="#000000" link="#000099" vlink="#cc0000" alink="#cc0000">
<h1><font size="-2">Hypertext Help with LaTeX</font><br><font color="#cc0000">Modes</font></h1>
<p>
When LaTeX is processing your input text, it is always in one of three
modes:
<ul>
<li><I>Paragraph</I> mode
<li><I>Math</I> mode
<li><I>Left-to-right</I> mode, called LR mode for short
</ul>
LaTeX changes mode only when it goes up or down a staircase to a
different level, though not all level changes produce mode changes.
Mode changes occur only when entering or leaving an environment, or
when LaTeX is processing the argument of certain text-producing
commands.
<h2>Paragraph mode</h2>
Paragraph mode is the most common; it's the one LaTeX is in when
processing ordinary text. In that mode, LaTeX breaks your text into
lines and breaks the lines into pages.
<p>
There
are also several text-producing commands and environments for making a
box that put LaTeX in paragraph mode. The box made by one of these
commands or environments will be called a
<a href="ltx-294.html">parbox</a>. When LaTeX is in
paragraph mode while making a box, it is said to be in inner paragraph
mode. The normal paragraph mode, in which LaTeX starts out, is called
outer paragraph mode.
<h2>Math mode</h2>
LaTeX is in math mode when it's generating a mathematical formula. It is
in math mode in the <a href="ltx-115.html#math">math</a>,
<a href="ltx-421.html">displaymath</a>, <a href="ltx-224.html">equation</a>,
and <a href="ltx-223.html"> eqnarray</a> environments.
<p>
In math mode letters are assumed to be math symbols and spaced accordingly.
Spaces in the input are ignored, except that spaces may be needed to
delineate the end of commands.
<h2>LR mode</h2>
In LR mode, as in paragraph
mode, LaTeX considers the output that it produces to be a string of
words with spaces between them. In LR mode, unlike paragraph and math modes,
spaces are not ignored; an input space creates an output space.
However, unlike paragraph mode, LaTeX
keeps going from left to right; it never starts a new line in LR mode.
Even if you put a hundred words into an
<a href="ltx-265.html"><tt>\mbox</tt></a>, LaTeX would keep
typesetting them from left to right inside a single box, and then
complain because the resulting box was too wide to fit on the line.
<p>
LaTeX is in LR mode when it starts making a box with an
<a href="ltx-265.html"><tt>\mbox</tt></a> command.
You can get it to enter a different mode inside the box - for example,
you can make it enter math mode to put a formula in the box.
<hr>
Also see <a href="ltx-115.html">Math Formulas</a><br>
Go to <a href="ltx-2.html">LaTeX Table of Contents</a><br>
<hr>
<address>
Revised: Sheldon Green, 31 May 1995.
</address>
</body>
</html>
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