### The Preamble of the LaTeX Input file

We describe the options available in LaTeX for specifying the overall style of a document.

A LaTeX document should begin with a \documentclass command and any text to be printed must be included between \begin{document} and \end{document} commands. The \begin{document} command is often preceded by commands that set the page-style and set up user-defined control sequences.

Here is a typical LaTeX input file:

\documentclass[a4paper,12pt]{article}
\begin{document}

This is the first paragraph of a typical document. It is
produced in a 12~point' size. A \emph{point} is a unit
of length used by printers. One point is approximately
$1/72$~inch. In a 12~point' font the height of the
parentheses is 12~points (i.e. about $1/6$~inch) and the
letter~m' is about 12 points long.

This is the second paragraph of the document. There are
also 10 point' and 11 point' styles available in LaTeX.
The required size is specified in the documentstyle'
command. If no such size is specified then the 10~point
size is assumed.

\end{document}


The syntax of the \documentclass command is as follows. The command begins with \documentclass and ends with the names of one of the available styles, enclosed in braces. The available styles are article, report, book and letter. Between the \documentclass'' and the name of the document style, one may place a list of options. These options are separated by commas and the list of options is enclosed in square brackets (as in the above example). The options available include the following:

11pt
Specifies a size of type known as eleven-point, which is ten percent larger than the ten-point type normally used.
12pt
Specifies a twelve-point type size, which is twenty percent larger than ten-point.
twocolumn
Produces two-column output.
a4paper
This ensures that the page is appropriately positioned on A4 size paper.

Typing simply \documentclass{article} will produce a document in ten-point type size. However the printed output will not be nicely positioned on A4 paper, since the default size is intended for a different (American) paper size.

Pages will be automatically numbered at the bottom of the page, unless you specify otherwise. This can be done using the \pagestyle command. This command should come after the \documentclass command and before the \begin{document} command. This command has the syntax \pagestyle{option}, where the option is one of the following:

plain
The page number is at the foot of the page. This is the default page style for the article and report document styles.
empty
No page number is printed.
Similar to the headings pagestyle, except that the material to go at the top of the page is determined by \markboth and \markright commands (see the LaTeX manual).
\documentclass[a4paper]{article}