XuanxuanQijingProblem200/Solution

Solution at a  

Order of play is important in this problem.

Wrong Order  

The reverse order is met by turn and allows ko. ( at a is met by at .) Compare with the above diagram; Black could connect underneath if not for the exchange of and .

Oversight by Go  

and without the other hane is met by (overlooked by Go Seigen), leading to ko again.