Gokyo Seimyo Volume 3 Problem 5 / Attempts

A vital point  

After black 1 white cannot resist with 2 etc. If they do white captures the entire corner after the sequence to 7, or...

ko  

Black risks a huge ko. However...

Best for both?  

White can give way with 2, and all black has accomplished is to capture 2 stones in gote. White can do better.

Force first  

White should force first with 1 & 3 before playing the vital point a. Continuing..

Ko left behind  

After white takes the two stones, if black tenuki's white is left with the ko after a to capture the rest of the corner.