# [OS X TeX] two-page split equation

Maarten Sneep maarten.sneep at xs4all.nl
Tue Apr 11 17:02:56 EDT 2006

On 11 Apr 2006, at 1:59, Alain Schremmer wrote:

>    \allowdisplaybreaks
>    \begin{align*}
>    …
>    \end{align*}

This provides me with a nice example of the meaning of 'scope',
another term you were not familiar with, IIRC. Scope in traditional
programming is the "reach" of a piece of code, most commonly a
variable: where can you use a variable in your code.

In TeX the scope (of changes) is limited to the current group. In the
piece of code I quoted, the change caused by \allowdisplaybreaks
applies to all code that comes after it, in he current group (usually
until \end{document}). However, if you want to apply it only to a
specific align environment, you have to put the environment inside a
group, and apply it there:

{ % this starts a group
\allowdisplaybreaks
\begin{align*}
…
\end{align*}
} % this closes the group, resetting TeX to not break displays.

Groups are delimited by curlies {} or \begingroup \endgroup pairs. In
LaTeX, \begin{...} and \end{...} also delimit groups.

As always there are exceptions to this rule, especially when defining
commands. Figuring those out is left as an excersise for the reader ;-)

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