Beginner Exercise 11 / Endgame Question

Gote  

After White is safe, having at least a seki. The question has arisen, what is the value of a play now at a?

Sente  

Actually, is a 7 point sente. (Assuming, as usual, that the left corner is Black territory.)

Sente again  

And then is another sente, worth 5 points. Now let's talk about a play at a.

Black first  

makes seki.

White first  

is a 5 point sente.