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<H2><A ID="SECTION00445000000000000000">
So what are control symbols and words?</A>
</H2><TT>
In typing a document, we can think of ourselves as
being in one of two distinct modes. We are either
typing <EM>literal text</EM> (which will just be set into neat
paragraphs for us) or we are typing text that will
be <EM>interpreted</EM> by L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X as an instruction
to insert a special symbol or to perform some action.
Thus we are either typing material that will go
straight into the document (with some beautification),
or we are giving commands to L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X.
</TT>
<P>
<TT>Some commands are implicit, in that we don't have to
do anything much extra. For instance, we command
L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X to end the present sentence by typing a
period (that doesn't follow a capital letter). These are
no so much commands as part of having to describe
the logical structure of a document.
</TT>
<P>
<TT>A <EM>control word</EM> is something of the form
<code></code>, where the command name
is a word made up only of the letters a to z and A to Z. A
<EM>control symbol</EM> consists of a <TT>\</TT>
followed by single symbol that is not a letter.
</TT>
<P>
<TT>Here are some examples:
</TT>
<UL>
<LI>we have met the control space symbol <code> </code> before,
</LI>
<LI>the commands to set symbols like </LI>
<LI><code></code> was a control symbol that told told L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X that
the very next period did really end the sentence,
</LI>
<LI><code>LATEX</code> is a control word that tell L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X to insert
its own name at the current point,
</LI>
<LI><code>&clubs#clubsuit;</code> instructs that a ♣ be inserted,
</LI>
<LI><code>£</code> inserts a £ symbol,
</LI>
<LI><code>§</code> inserts a ¶ symbol,
</LI>
<LI><code></code> makes the ensuing text <EM>be emphasised</EM>,
</LI>
</UL>
<P>
<TT>These examples show that control sequences can be used to
access symbols not available from the keyboard,
do some typesetting tricks like setting the word
L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X the way it does, and change the appearance of
whole chunks of text as with <code></code>. We'll be meeting
many more of these type of control sequences.
</TT>
<P>
<TT>Another enormously powerful class of control sequences is
those that accept <EM>arguments</EM>. They tell L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X to take the parts of text you supply and do something
with them—like make a fraction by setting the first
argument over the second and drawing a line of the
appropriate length between them. These are part of
what makes L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X so powerful, and here are some
examples.
</TT>
<P>
<UL>
<LI><code>