: ( 457)
This move is too restrained, and will end in a disaster for White.

:
Black's marked stones are secure already, so Black will end the Crosscut Sequence in sente.

:
Now, White has two vulnerable groups on the board - one on the left, one on the bottom - which both can get two eyes in gote only. White must be on her guard to do the right choice.

:
White's earlier move at occupied an important liberty of Black's group in the upper right. Therefore, it is correct for White to bring her group on the left edge to life.

:
Black reduces White's group on the bottom to one eye, and starts the semeai with his large group in the upper right.

:
White wins the semeai by one move.