Re: GiST indexing tuples

Matthew wrote:
> For instance, the normal B-tree index on (a, b) is able to answer queries
> like "a = 5 AND b > 1" or "a > 5". An R-tree would be able to index these,
> plus queries like "a > 5 AND b < 1".

Sorry in advance if this is a stupid question, but how is this better
than two index, one on "a" and one on "b"?  I supposed there could be a
space savings but beyond that?