(;C[How many ko threats can you squeeze out of this living group? Side note: The ko is worth less than this group.]AB[ka][jb][jc][kc][lc][ld][md][nd][od][pd][qd][qc][rb][qa]AW[kb][lb][ma][mc][nc][oc][pc][pb][qb][nb]LB[jf:0][lf:1][nf:2][pf:3][rf:4]AP[goproblems] (;B[rf]AW[pf][nf][lf];W[jf]C[Prove it!] (;B[oa];W[pa] (;B[na];W[ob] (;B[ja];W[la];B[na];W[oa]C[You got 'emRIGHT]) (;B[na];W[oa];B[ja];W[la]C[You got 'emRIGHT])) (;B[ja];W[la];B[na];W[ob];B[na];W[oa]C[You got 'emRIGHT]) (;B[ob];W[la]C[Only 2 Threats])) (;B[ja];W[oa]C[Only 1 threat]) (;B[pa];W[oa]C[Only 1 Threat]) (;B[ob]C[Not Threat]) (;B[na]C[Not Threat])) (;B[pf]PL[W]AB[oa]CR[oa]C[You are White now! Black just played the 1st ko threat. What would you do?];W[pa];B[ja]C[And that's 2...];W[la];B[na]C[3...];W[ob];B[na]C[4 at last!]) (;B[nf]PL[W]AB[oa]CR[oa]C[You are White now! Black just played the 1st ko threat. What would you do?];W[pa];B[ja]C[And that's 2...];W[la];B[na]C[And 3!]) (;B[lf]PL[W]AB[oa]CR[oa]C[You are White now! Black just played the 1st ko threat. What would you do?];W[pa];B[ja]C[And that's 2!]) (;B[jf]AB[oa]CR[oa]C[You chose 0 ko threats, but if Black plays the marked move White must answer or die - so that is clearly a ko threat.]))