This diagonal is a fairly common first move in these capturing races - it doesn't take up internal liberties and it prevents Black from moving at either marked point before defending that stone - one move. Effectively it creates a double shortage of liberties for Black, thus White wins the capturing race by one turn.
and
appears to create a seki, but this is not a seki. Because the group of stones containing
is dead, so all the white stones are dead.
In fact, can even play tenuki. The reason behind this is left as an exercise for the reader.
at
-- ProtoDeuteric
Bill: loses 1 1/3 points: 1 point for the the point on
, and 1/3 point for the stone left in atari in the ko.