A KGS 16 kyu found the correct move in rengo. So if you do not solve this you are weaker than16k.... :-)
Sente is not important, ko threats are not important.
(;AB[br]AB[cr]AB[dq]AW[ho]AW[bp]AW[bq]AB[fo]AB[go]AB[eo]AW[gp]AW[fp]AW[ep]AW[hp]AW[dp]AW[co]AW[cq]AB[do]AB[eq]AB[fq]AB[gq]AB[hq]AW[dl]AW[jp]AB[gn]AB[hn]AW[in]AW[hm]AB[fn]AW[en]AB[hk]AB[gk]AB[fk]AB[ek]AW[dk]AW[em]AW[el]AB[lq]AB[ar]AB[lp]AB[lo]AB[kn]AB[km]AB[jl]AB[ik]AB[lr]AB[dn]AB[dm]AW[cm]AW[cn]AW[cl]AW[aq]C[Black to play. What is the best endgame here?]AP[goproblems]
(;B[io]
(;W[ip]C[White responds aggressively! How do you answer?];B[im];W[jo];B[gm]C[White can invade the bottom now, but black saved a lot of stones.
Playing the marked move was not optimal for White.RIGHT]TR[ip])
(;W[im]C[Do not play A or B, those moves are not worth any points...]LB[fl:A]LB[gl:B];B[ip];W[cp];B[jn]C[Good!RIGHT]))
(;B[iq];W[ip]C[Compare with the solution.])
(;B[im];W[gm];B[io];W[fm];B[ip];W[jo];B[iq];W[jn]C[Worse than the solution.]))