</code> causes L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X to
start a new chapter with name ``The Beginning'', number
it in sequence, typeset the chapter heading in a suitable
font, and make an entry in the table of contents,
</LI>
<LI><code>words</code> causes <!– MATH
–>
<IMG
STYLE="height: 163.54ex; vertical-align: -0.10ex; " SRC="img1.png"
ALT="
"> to
be overlined,
</LI>
<LI><code>a+bc+d</code> sets the given two argument as
a fraction, doing most of the dirty work for us: <!– MATH
–>
<IMG
STYLE="height: 2.10ex; vertical-align: 146.36ex; " SRC="img2.png"
ALT="
">,
</LI>
<LI><code>[5]a+b</code> typesets the fifth-root of <I>a</I> + <I>b</I>,
like this: <!– MATH
–>
<IMG
STYLE="height: 1.98ex; vertical-align: 146.97ex; " SRC="img3.png"
ALT="
">. The <TT>5</TT> is in square brackets
instead of braces because it is an optional argument and
could be ommited all together (giving the default of square root),
</LI>
</UL>
<P>
<TT>Mandatory arguments are given enclosed by braces, and
optional arguments enclosed by square brackets. Each
command knows how many arguments to expect, so
you don't have to provide any indication of that.
</TT>
<P>
<TT>We have actually jumped the gun a little. The above examples
include examples of <EM>mathematical</EM> typesetting, and we
haven't yet seen how to tell L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X that it is typesetting
maths as opposed to some other random string of symbols
that it doesn't understand either. We'll come to mathematical
typesetting in good time.
</TT>
<P>
<TT>We need to dwell on a T<SMALL>E</SMALL>Xnicality for a moment. How does
L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X know where the name of a control sequence ends?
Will it accept both <code>£3</code> and <code>£3</code>
in order to set £3, and will <code></code>
and <code>Walrus</code> both be acceptable in order to
get <EM>Walrus</EM>? The answer is easy when you remember
that a control word consists only of alphabetic characters,
and a control symbol consists of exactly one nonalphabetic
character.
</TT>
<P>
<TT>So to determine which control sequence you typed,
L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X does the following:
</TT>
<OL>
<LI>when a <TT>\</TT> character is encountered, L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X knows
that either a control symbol or a control word will follow.
</LI>
<LI>If the <TT>\</TT> is followed by a nonalphabetic character,
then L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X knows that it is a control <EM>symbol</EM>
that you have typed. It then recognises which one it was,
typesets it, and goes on to read the character which follows
the symbol you typed.
</LI>
<LI>If the <TT>\</TT> is followed by an alphabetic character, then
L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X knows that it is a control word that you have typed.
But it has to work out where the name of the control word ends
and where the ensuing text takes over again. Since only alphabetic
characters are allowed, L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X reads everything up to
just before that first
nonalphabetic character as the control sequence name. Since
it is common to delimit the end of a control word by a space,
L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X will <EM>ignore</EM> any space that follows a control
word, since you want that space treated as end-of-control-word
space rather than interword space.
</LI>
</OL>
<P>
<TT>This has one important consequence: The character in the input
file immediately after a control symbol will be ``seen'' by L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X,
but <EM>any space following a control word will be
discarded and never processed.</EM> This does not affect one much if you adopt
the convention of always typing a space after a control sequence name.
</TT>
<P>
<TT>There is a rare circumstance where this necessitates a little extra work
and thought, which we illustrate by example:
</TT>
<P>
<TT>0.1</TT><PRE>
If we type a control word like LATEXin the running text
then we must be cautious, because the string of spaces that
come after it will be discarded by the LATEX system.
</PRE><TT>
which produces the output
</TT>
<P>
<P></P>
<TT>0.10.8<FONT SIZE="-1">If we type a control word like L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>Xin the running text
then we must be cautious, because the string of spaces that
come after it will be discarded by the L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X system.
</FONT></TT>
<P></P>
<P>
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