This puzzle was created by Barry C. Silk and edited by Peter Gordon.
Themeless. There were a number of difficult clues sprinkled about which slowed solving down, but nothing that would bring you to a grinding stop. One thing which I had no idea of but has a commonplace answer is the clue [Repeated action in a mathematician's random walk] in 23A, and the answer is
COINTOSS.
In order to complete the fill
CLI needed to be in 23D [One-twentieth of
MMMXX] and my friend John wondered if in the old Roman days they had a system for doing math in Roman Numerals. Anybody know? I just convert to cardinal numbers, do the math and convert back again. How did they do it then?
There were two things in this puzzle I thought were really difficult: 8D [Another name for the sugar apple] with the answer
SWEETSOP and 55D [Place in a Robert Redford movie] with the answer ETTA.
55D - Place in a Robert Redford movie
It turns out that the role Katharine Ross played in
"Butch
Cassidy and the
Sundance Kid" was... Etta Place
About the
Sweetsop apple--clued as [Another
name for the sugar apple]: It is a semi-evergreen shrub
which grows six to eight meters tall. It bears edible fruit:
The fruit is usually round, slightly pine cone-like,
6-10 cm diameter and weighing 100-230 g, with a
scaly or lumpy skin. There are variations in shape
and size. The fruit flesh is sweet, white to light
yellow, and resembles and tastes like custard. The
edible portion coats the seeds generously; a bit
like the gooey portion of a tomato seed. Sugar-apple
has a very distinct, sweet-smelling fragrance. The
texture of the flesh that coats the seeds is a bit
like the center of a very ripe guava (excluding the
seeds). It is slightly grainy, a bit slippery, very
sweet and very soft. The seeds are scattered through
the fruit flesh; the seed coats are blackish-brown,
12-18 mm long, and hard and shiny.
It is grown in the tropics and warmer subtropics. I've never heard of it before. The picture at the top of this post is of the fruit of this plant.