The FunctionAdvisor(function_classes) command returns all class names for which information is available.

The 26 functions in the "elementary" class are:

* Partial match of "ortho" against topic "orthogonal_polynomials".
The 7 functions in the "orthogonal_polynomials" class are:

* Partial match of "classify" against topic "classify_function".
* Partial match of Gegen against topic GegenbauerC.
GegenbauerC belongs to the subclass "orthogonal_polynomials" of the class "2F1" and so, in principle, it can be related to various of the 26 functions of those classes - see FunctionAdvisor( "orthogonal_polynomials" ); and FunctionAdvisor( "2F1" );