net -- format for printing, as a net

This function is the primary function called upon by << to format expressions for printing. The default method provided by the system is to convert o to an Expression with expression and then to convert that to a Net.

A new method for formatting expressions of type T may be installed as follows:

The function provided by the user should return a Net or a String.

There are various such methods for formatting, but we don't document them separately.