When I withdrew PEP 577, I intended to write up a new alternative
to both it and PEP 572, but the replacement never reached a state
where I liked it enough to post it.
So this amends the withdrawal notice to make it clear that there's
no further alternative planned.
Competing proposal for PEP 572 that focuses on allowing
augmented assignments as expressions, and treats
"NAME := EXPR" primarily as an explanatory tool for
the updated augmented assignment semantics.