Black just played the marked stone, not letting white to connect her stone.
It's the endgame and w is behind. Black doesn't have more ko threats than white.
what damage can w do in return?
(;AW[rq]AW[rr]AW[qq]AW[pr]AW[or]AW[os]AW[oq]AW[op]AB[pp]AB[qp]AB[rp]AB[oo]AB[on]AB[pn]AB[qn]AB[rm]AB[rl]AB[rk]AB[ql]AW[qm]AW[pm]AW[om]AW[pl]AW[pk]AW[qk]AW[qj]AW[rj]AW[sk]AB[mo]AB[np]AW[mm]AW[sn]AB[so]AW[si]AW[ri]AW[rh]TR[so]AP[goproblems]
(;W[ro];B[sp];W[rn];B[qo];W[sm];B[sl];W[rn]C[Ko - but quite a big one.
Well done!RIGHT];B[sj]C[Ko - but quite a big one.
Well done!RIGHT])
(;W[sl];B[rn])
(;W[sm];B[rn])
(;W[rn];B[ro]))