tderz: once the liberty at is gone,
White can capture at least the 4 left stones by atari-ing at .
Having said this,
any black stone at at any of the points occupied by to ,
or those a, b, which would pt , in atari,
would defend against this threat.
tderz: thus, the possible defending moves are:
a to g.
Of these, g looks the least attractive,
b the most dangerous (3 ko threats);
a looks quite ok, as one is relatively safe from an attack at p (rests peep c with possible false eye b).
c has one 2 threats (f, d);
f might be in danger after peep c, then jump to p (defense b, q might cost points).
My conclusion: best answer depends on surrounding & actual game situation.
Bill: Yes, but don't you think that a will usually be best? d still allows two ko threats.
tderz: yes, normally agreed, as snapback-test can be answered by (direct life), even if a white stone is present at .
Usually it depends on the actual game situation.
tderz: this allows for making a false eye if is safe.
tderz: Hence, sometimes could be safest (even in the presence of an -> Black has 2 eyes at f and d)