In 
, the main way of controlling the format of your
document is by using matched pairs of \begin{ } and
\end{ } commands. In terminology, such a
matched pair is an environment: it specifies how the
text which it encloses is to appear.
There are
environments to center text, to typeset a theorem, a
numbered list, a table, etc.
Environments may be nested. It is important that the
\end{ } statements appear in the opposite order of
the \begin{ } statements; that is, any \end{ }
command must end the environment begun by the most recent
\begin{ } command.
If you want to change the type style of a big chunk of text (more than a paragraph, to be precise), you must declare an environment:
...the following condition:
\begin{itshape}
The polynomial $p(t)$ splits...
\end{itshape}
yields
...the following condition:
The polynomial p(t) splits...
Note that you do not have to type the backslash before the typestyle
name when you are using the environment declaration \begin{ } and
\end{ } commands, as you do when you use the typestyle name as a
command itself. An alternative (quicker) way to declare environements is to
enclose the environment name preceded by a backslash along with the text
to be affected in braces. Thus the above text could have been
alternatively entered as (using the ``global form'' listed in Section 6.1):
{\itshape The polynomial $p(t)$ splits ...}