minimum operators for b-tree, r-tree

When creating a new data type, what are
the operators absolutely necessary for that
type to particpate in a btree index?

I know you need a "compare" that says = < or >=
so does that mean that those three operators
are the ones required?

If you also know that answer for our implementation
of R-trees that would also be helpful.
I believe it is intersects and overlaps but
it would be nice to get confirmation.

Thanks,
elein
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