Re: SLOPE - Planner optimizations on monotonic expressions.

> There were too many possibilities for my brain to enumerate, so I scripted
> the
> extraction and presentation of that in regress/sql/slope.sql in commit 0005.

Apologies, I forgot to reply to this earlier, the new NULL handling
looks good. Nice test!

I found one more corner case with infinities (same applies also with
negative infinity):

CREATE TABLE t8 (x float8);
INSERT INTO t8 VALUES (-2), (-1), (0), (1), (2);
CREATE INDEX t8_x_idx ON t8 (x);
ANALYZE t8;

SET enable_seqscan = off;
SELECT x, x * 'Infinity'::float8 AS f FROM t8 ORDER BY x * 'Infinity'::float8;

SET enable_indexscan = off;
SET enable_indexonlyscan = off;
SET enable_seqscan = on;
SELECT x, x * 'Infinity'::float8 AS f FROM t8 ORDER BY x * 'Infinity'::float8;