Elizabeth: After wA17, bA16, wA12, black has a tesuji at bA18.
After the tesuji if wB17 then bB19 starts a ko.
If, instead, white takes with wA19, bB17 starts another ko which is dangerous for white.
Ivan Detkov: I agree. Although the risk of ko is asymmetric, it could be a viable strategy. I corrected the sequence.
StephaneLamy: I don't see why A17 (or A3 in the sgf file) is inferior to the correct solution A18.
In fact it seems with A17 one can get one more point (in gote)
After wA17, bA16, wA12, black has a tesuji at bA18. After the tesuji if wB17 then bB19 starts a ko. If, instead, white takes with wA19, bB17 starts another ko which is dangerous for white.