DietersMistakesIn2021/Solution 58
is an example of surround in sente which is one of the patterns in this mistake analysis series. If
elsewhere, then
is big. Black can live but
takes 15 points in sente because of a.
Compared to
answering locally, the difference goes up to more than 20 points, so that
can be considered sente.
is premature. Black can break through the lines and there's bad aji at the marked point.