(;GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2] RU[Japanese]SZ[19]KM[6.50] PW[dr]PB[ect]AW[ra][mb][qb][kc][mc][oc][qc][dd][ld][nd][pd][me][pe][cf][mf][pf][jg][kg][lg][og][qg][nh][oh][di][pi][fj][gj][hj][jj][pj][hk][jk][pk][il][jl][jm][kn][on][qn][lo][mo][ro][rp][jq][kq][lq][mq]AB[na][oa][qa][nb][pb][rb][fc][hc][jc][lc][nc][pc][jd][od][fe][oe][nf][mg][ng][kh][lh][mh][ph][mi][ni][oi][kj][oj][dk][fk][gk][ik][kk][hl][cm][gm][im][jn][io][ko][cp][kp][lp][mp][pp][eq][hq][nq][qq][rq][mr][nr]C[Black has just captured the ko at Q19. Find White's largest ko threat.]PL[W]MA[pa] (;W[np]CR[np] ;B[pa]CR[pa]C[If Black fills, what is White's follow-up?] ;W[jo]CR[jo] ;B[jp]CR[jp]C[Black clearly doesn't see O4 as a reasonable ko threat. Convince him you were right.] ;W[ip]CR[ip] ;B[jo]CR[jo] ;W[ho]CR[ho] ;B[in]CR[in] ;W[hm]CR[hm] ;B[hn]CR[hn] ;W[gn]CR[gn] ;B[hm]CR[hm] ;W[fm]CR[fm] ;B[gl]CR[gl] ;W[ek]CR[ek] ;B[fl]CR[fl] ;W[el]CR[el]C[RIGHT]) (;W[jo]CR[jo] ;B[pa]CR[pa]C[Black fills, clearly indicating that he thinks your invasion doesn't have legs to stand on. Convince him.] (;W[np]CR[np] ;B[jp]CR[jp] ;W[ip]CR[ip] ;B[jo]CR[jo] ;W[ho]CR[ho] ;B[in]CR[in] ;W[hm]CR[hm] ;B[hn]CR[hn] ;W[gn]CR[gn] ;B[hm]CR[hm] ;W[fm]CR[fm] ;B[gl]CR[gl] ;W[ek]CR[ek] ;B[fl]CR[fl] ;W[el]CR[el]C[RIGHT]) (;W[jp]CR[jp] ;B[np]CR[np]C[Even despite the remaining atari in White's favor at K6, you should be able to do better.]) (;W[in]CR[in] ;B[jp]CR[jp]C[White has only made a small dent in Black's moyo, and your stones at the bottom are still cut from the top. You can do better.])) (;W[of]CR[of] ;B[ne]CR[ne]C[Black would answer this, but it's not the biggest ko threat. If White recaptures the ko at Q19, Black starts a second ko at N16.]) (;W[ne]CR[ne] ;B[of]CR[of]C[Black would answer this, but it's not the biggest ko threat. If White recaptures the ko at Q19, Black captures to make an eye at Q13.]) (;W[pa]CR[pa]C[NOTTHIS]))