In Gokyo Shumyo, Section 1, Problem 75 / Solution, the following response is untreated:
I believe that the
/
exchange is unnecessary, and that
at
already forces
. Otherwise
at
seems to live or get out very quickly. So here, IMHO, is the main line.
The variations at
are similar to Gokyo Shumyo, Section 1, Problem 75 / Solution.
Other responses at
run into shortage of liberties.