operators and indexes - Mailing list pgsql-hackers

I have defined various operators for some user defined types.  How do
I use them for setting up an index on the types?

The naive approach yields the following
ERROR:  DefineIndex: type geocentric_point has no default operator class

so presumably one must define a default operator.  How is this done
and what exactly are the semantics of a default operator?

Thanks for your help.

Cheers,
Brook