removes the main aji in the corner.
Later, -
is sente.
The result is +9 (for Black).
fills at
.
There is no unique solution, but I think that is psychologically best.
is not that obvious.
Next, -
takes kikashi in the corner.
Now, is tesuji, preventing ko or seki and allowing
.[1]
Later, -
is sente.
The result is +4.
So this is White's 5-point sente.
In the game, both players overlooked it.
[1]
takes at
.
If hanes,
should normally be at a.
is immune to immediate capture, because of snapback.
Now Black can make a seki at a or make a picnic ko for White at b.