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Mathematica Notebooks
Every Mathematica notebook is a complete interactive
document which combines
text, tables, graphics, calculations, and other elements.
Your notebooks are automatically organized in a hierarchy of cells. You
can close groups of cells so you see only their headings. You can use
hyperlinks to jump within a notebook or between notebooks. You can assign
each cell a style from a style sheet. Your Mathematica notebooks
are automatically retargeted for screen or printout--optimizing fonts and
layout for each medium. Mathematica provides hundreds of options
that allow you to give notebooks any look you want and to generate full
publication-quality documents.


Like other objects in Mathematica, the cells in a notebook, and in
fact
the whole notebook itself, are all ultimately represented as
Mathematica
expressions. With the standard notebook front end, you can use the command
Show Expression to see the text of the Mathematica
expression that
corresponds to any particular cell.
The Mathematica language can be used to specify all aspects of
notebooks. This is how Mathematica represents a cell.

This tells Mathematica to print three cells in subsection style.