:
Even if White's upper group on the left side lost a liberty, e.g. by the exchange of / , and had six liberties now, there would be no need to answer this atari locally. This is because Black has connected the hanezeki's tail already.

:
White occupies a liberty of Black's connected group on the lower edge. Please note that this group now has four liberties left, as many as White's centre group.

:
White wins the semeai by one move.

///:

:
It does not help Black either to re-capture the ko. White's centre group has one liberty too many.

:
Again, White is the decisive step faster.