Operator COMMUTATOR - how does postgresql use this information

Does PostgreSQL use the COMMUTATOR property of an operator to determine
if flip-flopped arguments can be collapsed.

I used to think it did until someone pointed it doesn't - For example
in the below

SELECT b.*
FROM boszip b INNER JOIN landparcels l
ON (b.the_geom && l.the_geom AND l.the_geom && b.the_geom AND
l.the_geom && b.the_geom )
WHERE l.gid = b.gid and b.gid = l.gid
limit 1


If I look at the query plan - I see the plan has reduced things down to

l.gid = b.gid AND (b.the_geom && l.the_geom AND l.the_geom &&
b.the_geom)

Why is (b.the_geom && l.the_geom AND l.the_geom && b.the_geom) not
reduced down to just

b.the_geom && l.the_geom

even though && is defined as the commutator of &&?

Thanks,
Regina

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