One basic problem with this and other yose problems is that they are not well defined. What lies to the left of the diagram? It matters.
There are some standard assumptions.
We can assume that the surrounding area is Black's territory (or almost so). That is a natural assumption, and the answers to yose problems bear out that the authors are making it. (If not, we would see some White stones outside.)
But how strong is Black outside? In this variant prevents White from intruding too far into Black's territory. In this case the solution is very like the solution given.
Now the local temperature has dropped to 1 point.
is a three-point sente.
Because of shortage of liberties, after White must play at .
Without the stone to the left (in the variant) below threatens to make a significant incursion into Black's territory.
Normally in yose problems such a move is treated as sente. Let's do that here. After , White has 10 points of territory. Since playing a sente play does not change the count, let's take that as the original count.
- is a five-point reverse sente play.
That assumes, of course, that at 3 would be sente, eliciting . Does that make sense?
If Black fails to answer , - is sente, then later - , and later - . So at 3 would be a 7 point reverse sente play. That confirms that is a 5 point sente play.
Note: The absence of a stone to the left, as in the variant, indicates that there is no such stone to prevent a deep incursion. If there were, it would have been shown.
This is not just an apparent convention with yose problems. It follows general principles of interpretation shared by many cultures.