Black just played the marked stone to give a dead shape to white however white still can live.
There are many variations, therefore i made it like a multiple-choice question. If there is missing variation please let me now.
(;AW[ls]AW[mr]AW[ns]AW[pr]AW[pq]AW[pp]AW[qp]AW[op]AW[oo]AW[no]AW[mp]AW[mq]AW[lq]AW[kq]AW[jq]AW[jp]AW[jo]AW[io]AW[hn]AW[hm]AW[il]AW[jk]AW[lk]AW[ll]AW[lm]AW[mk]AW[nk]AW[mi]AW[nj]AW[pi]AW[pj]AW[qk]AW[rl]AW[qj]AW[qn]AW[pn]AB[po]AB[qo]AB[ro]AB[rp]AB[qq]AB[qr]AB[om]AB[on]AB[nn]AB[mn]AB[kn]AB[ln]AB[in]AB[jn]AB[mo]AB[lr]AB[kr]AB[jr]AB[ir]AB[hp]AB[ho]AW[hj]AW[hi]AW[hh]AW[hg]AW[le]AB[kg]AB[kh]AB[ig]AB[ih]AB[ii]AB[ij]AB[jj]AB[kj]AB[lj]AB[mj]AB[ni]AB[oi]AB[oh]AB[og]AB[oj]AB[ok]AB[pk]AB[pl]AB[ql]AB[ml]AB[nl]AB[mg]AB[lg]AW[ph]AW[pg]AW[of]AW[nf]AW[ng]AW[nh]AW[gl]AB[mh]AW[li]AW[ps]AW[os]AB[lp]AB[hk]AB[sr]AB[nq]C[White to liveFORCE]TR[nq]AB[gr]AW[fm]AW[jg]AB[jf]AW[if]AW[ie]AW[ke]AW[rj]AW[me]AW[jd]AW[jh]AW[fj]AP[goproblems]
(;W[rn];B[pm]C[FORCE]
(;W[rs]
(;B[rr]C[Play T5 only if you think it kills the cornerCHOICEFORCE]
(;W[qs];B[rm]
(;W[sm];B[so]C[FORCE]
(;W[qm];B[sq]C[FORCE]
(;W[mm];B[nm]C[FORCE]
(;W[kf];B[jl]C[tesuji ! But the bottom white group still can live...FORCE]
(;W[jm];B[kl]
(;W[km];B[im];W[kk];B[ik]C[]
(;W[ko]C[];B[lo]
(;W[kp]C[RIGHT])
(;W[hl];B[jl])
(;W[jl];B[hl]))
(;W[jl];B[hl])
(;W[hl];B[jl])
(;W[kp];B[hl];W[lo];B[jl];W[ko]C[RIGHT]))
(;W[kk];B[km]TR[ik]TR[im]))
(;W[kl];B[jm]TR[ik]TR[kk])
(;W[kk];B[ik];W[jm];B[km];W[kl];B[jl])
(;W[ik];B[kk]))
(;W[jm];B[kf]))
(;W[kf];B[mm])
(;W[jm];B[mm]))
(;W[sq];B[qm]))
(;W[so]
(;B[qm])
(;B[sp];W[sm];B[qm]))
(;W[sn];B[sm]))
(;W[so]C[];B[sp]C[FORCE];W[qs];B[rm]C[T5 doesn't work];W[sm];B[qm]))
(;B[qs]C[black mistake];W[so]
(;B[sp];W[rq])
(;B[rq];W[sp]))
(;B[rm]
(;W[sm];B[rr])
(;W[rr];B[rq];W[sm]
(;B[so];W[qm])
(;B[qs];W[qm];B[so]))
(;W[so]
(;B[rq];W[sm];B[sp];W[qm];B[qs])
(;B[sq];W[rr]))))
(;W[mm];B[nm]C[FORCE]
(;W[rs];B[rr]C[Play T5 only if you think it kills the cornerFORCE]
(;W[qs];B[rm]C[FORCE]
(;W[sm];B[so]C[FORCE]
(;W[sq];B[qm])
(;W[qm];B[sq]
(;W[kf];B[jl]C[tesuji ! But the bottom white group still can live...FORCE]
(;W[jm];B[kl]
(;W[km];B[im];W[kk];B[ik]C[]
(;W[ko]C[];B[lo]
(;W[kp]C[RIGHT])
(;W[hl];B[jl])
(;W[jl];B[hl]))
(;W[jl];B[hl])
(;W[hl];B[jl])
(;W[kp];B[hl];W[lo];B[jl];W[ko]C[RIGHT]))
(;W[kk];B[km]TR[ik]TR[im]))
(;W[kl];B[jm]TR[ik]TR[kk])
(;W[kk];B[ik];W[jm];B[km];W[kl];B[jl])
(;W[ik];B[kk]))
(;W[jm];B[kf])))
(;W[so];B[sp];W[sm];B[qm])
(;W[sn];B[sm]))
(;W[so];B[sp]C[FORCE];W[qs];B[rm]C[T5 doesn't work];W[sm];B[qm]))
(;W[kf];B[jl]C[tesuji ! But the bottom white group still can live...FORCE]
(;W[rs];B[rr]C[Play T5 only if you think it kills the cornerFORCE]
(;W[qs];B[rm]C[FORCE]
(;W[so];B[sp];W[sm];B[qm])
(;W[sn];B[sm])
(;W[sm];B[so]C[FORCE]
(;W[sq];B[qm])
(;W[qm];B[sq]
(;W[jm];B[kl]
(;W[km];B[im];W[kk];B[ik]C[]
(;W[ko]C[];B[lo]
(;W[kp]C[RIGHT])
(;W[hl];B[jl])
(;W[jl];B[hl]))
(;W[jl];B[hl])
(;W[hl];B[jl])
(;W[kp];B[hl];W[lo];B[jl];W[ko]C[RIGHT]))
(;W[kk];B[km]TR[ik]TR[im]))
(;W[kl];B[jm]TR[ik]TR[kk])
(;W[kk];B[ik];W[jm];B[km];W[kl];B[jl])
(;W[ik];B[kk]))))
(;W[so];B[sp]C[FORCE];W[qs];B[rm]C[T5 doesn't work];W[sm];B[qm]))
(;W[jm];B[kl]C[FORCE]
(;W[km];B[im]C[FORCE];W[kk];B[ik]C[FORCE]
(;W[rs];B[rr]C[Play T5 only if you think it kills the cornerFORCE]
(;W[qs];B[rm]C[FORCE]
(;W[sm];B[so]C[FORCE]
(;W[sq];B[qm])
(;W[qm];B[sq]C[FORCE]
(;W[ko]C[];B[lo]
(;W[kp]C[RIGHT])
(;W[hl];B[jl])
(;W[jl];B[hl]))
(;W[jl];B[hl])
(;W[hl];B[jl])
(;W[kp];B[hl];W[lo];B[jl];W[ko]C[RIGHT])))
(;W[so];B[sp];W[sm];B[qm])
(;W[sn];B[sm]))
(;W[so];B[sp]C[FORCE];W[qs];B[rm]C[T5 doesn't work];W[sm];B[qm]))
(;W[hl];B[jl])
(;W[jl];B[hl])
(;W[qm];B[sn];W[rm];B[hl]C[R7 was the idea, but black is alive with T6])
(;W[rq];B[rr]
(;W[jl];B[hl])
(;W[hl];B[jl])))
(;W[kk];B[km]
(;W[ik];B[im])
(;W[im];B[ik])))
(;W[kk];B[ik];W[jm];B[km])
(;W[kl];B[jm]TR[ik]TR[kk])
(;W[qm];B[sn];W[rm];B[ik])
(;W[rq];B[rr]
(;W[kl];B[jm]TR[ik]TR[kk])
(;W[jm];B[kl]
(;W[km];B[im];W[kk];B[ik]TR[hl]TR[jl]C[miai]
(;W[jl];B[hl])
(;W[hl];B[jl]))
(;W[kk];B[ik];W[km];B[im]))
(;W[kk];B[ik];W[jm];B[km])))
(;W[qm];B[sn];W[rm];B[kf]C[All black stones are alive so white is dead])
(;W[jm];B[kf])
(;W[rq];B[rr]
(;W[kf];B[jl]
(;W[kl];B[jm]TR[ik]TR[kk])
(;W[jm];B[kl]
(;W[km];B[im];W[kk];B[ik]TR[hl]TR[jl]C[miai]
(;W[jl];B[hl])
(;W[hl];B[jl]))
(;W[kk];B[ik];W[km];B[im]))
(;W[kk];B[ik];W[jm];B[km]))
(;W[jm])))
(;W[qm];B[sn];W[rm];B[mm])
(;W[kf];B[mm])
(;W[rq];B[rr]
(;W[mm];B[nm]C[FORCE]
(;W[kf];B[jl]
(;W[kl];B[jm]TR[ik]TR[kk])
(;W[jm];B[kl]
(;W[km];B[im];W[kk];B[ik]TR[hl]TR[jl]C[miai]
(;W[jl];B[hl])
(;W[hl];B[jl]))
(;W[kk];B[ik];W[km];B[im]))
(;W[kk];B[ik];W[jm];B[km]))
(;W[jm]))
(;W[kf];B[mm])
(;W[jm];B[mm]))
(;W[jm];B[mm]))
(;W[rs];B[rn])
(;W[mm];B[rn])
(;W[kf];B[rn])
(;W[rq];B[rr];W[rn];B[pm]C[FORCE]
(;W[mm];B[nm]C[FORCE]
(;W[kf];B[jl]
(;W[kl];B[jm]TR[ik]TR[kk])
(;W[jm];B[kl]
(;W[km];B[im];W[kk];B[ik]TR[hl]TR[jl]C[miai]
(;W[jl];B[hl])
(;W[hl];B[jl]))
(;W[kk];B[ik];W[km];B[im]
(;W[jl];B[hl])
(;W[hl];B[jl])))
(;W[kk];B[ik];W[jm];B[km]))
(;W[jm]))
(;W[kf];B[mm])
(;W[jm];B[mm]))
(;W[jm];B[rn]))