Open coded (NOT x) as (IF x #F #T).

Open coded (NOT x) as (IF x #F #T).

In all likelihood any NOTs left at this stage are in value expressions
(as opposed to predicates) and this rewrite prevents nastiness when X
is a predicate, as in
	(lambda (x y) (<= x y))
which is
	(lambda (x y) (not (&> x y)))
This rewrite forces the coercion from predicate to value up to the
whole body.