 manipulate the new category of state information. Each of these
methods are templated with the name of the custom data type.

<p>For example, a common case is the need to track data associated with a
symbolic expression; a map type is the most logical way to implement this. The
key for this map will be a pointer to a symbolic expression
(<tt>SymbolRef</tt>). If the data type to be associated with the symbolic
expression is an integer, then the custom category of state information would be
declared as

<pre