Index scan troubles

Hi,

I'm having a hard time using an index scan. So far, I've done quite well 
with ScanKeyInit for equality searches. But now I need to scan an index 
from a given starting point. Something like:
   (x, y, z,...) > (const, const, const,...)

For the equality operatior, I've used get_sort_group_operators() in 
combination with get_opcode() to pass that on as the sk_func of the scan 
key. I slowly begin to doubt if that's correct at all.

While it works for equality scans, it does somehow not work for for 
BTGreaterStrategy. What am I missing?

I do have the following: an indexStruct on the index (primary key) I 
want to use, a TupleDescriptor for the relation I want tuples from and 
of course the list of constants (datums) to compare against. I want to 
do an index scan to retrieve tuples from that given lower bound upwards 
(or forwards).

I don't quite grok all the opfamily and opclass things, yet. Hints and 
pointers on where to read on greatly appreciated. A virtual beer for 
sample code. ;-)

Regards

Markus Wanner