My first problem. For beginners...
This is a variation off something from a game I played on KGS. In the game, he (black) had one more eye than in this problem, but still lost part of the group. Considering he was 11k and there was no time limit, I was surprised he missed it.
Edit: Thanks for the corrections from Dudzik on some variations.
(;AP[goproblems]AB[qe]AB[qf]AB[pf]AB[of]AB[oh]AB[ph]AB[qi]AB[ri]AB[si]AB[rg]AB[sj]AW[rl]AW[sk]AW[rj]AW[qj]AW[pi]AW[oi]AW[oe]AW[pe]AW[pd]AW[qd]AW[re]AW[rd]AW[qg]AB[og]AW[nf]AW[ng]AW[nh]AW[ni]AW[nd]C[White to kill. In the actual game, black had one more eye, but still gave up part of his group.](;W[sg](;B[sf](;W[rf];B[sh](;W[qh]TR[ph]TR[oh]TR[og]TR[of]TR[pf]TR[qf]TR[qe]C[AtariRIGHT])(;W[se];B[qh];W[sg]C[Ko])(;W[rh])(;W[pg];B[qh]))(;W[sh];B[rf](;W[qh];B[rh])(;W[rh];B[qh])(;W[pg];B[qh]))(;W[rh];B[rf](;W[qh];B[sh];W[sg]C[RIGHT])(;W[sh];B[qh]))(;W[qh];B[rf](;W[rh];B[sh];W[sg]C[RIGHT])(;W[sh];B[rh])(;W[se];B[rh])))(;B[qh](;W[sh];B[sf];W[rf];B[rh](;W[sg]C[RIGHT])(;W[sh];B[sg])(;W[se];B[sg]))(;W[rf];B[sh](;W[rh]C[Ko in your favor, but you can do better.])(;W[sf];B[pg]))(;W[rh];B[sh];W[rf];B[sf];W[se];B[sg])(;W[sf];B[sh];W[rf];B[pg])))(;W[qh];B[rh](;W[rf](;B[pg](;W[sg]C[CyclopsRIGHT])(;W[qg];B[qh];W[sg]C[Okay, but keep in mind skipping R13 was fineRIGHT])(;W[qh];B[qg];W[sg]C[Okay, but keep in mind skipping R12 was fineRIGHT]))(;B[sg];W[pg]C[RIGHT]))(;W[sg];B[sf];W[rf]C[Atari. White can only get one eye with wQ13 which is 1 point gote. Black doesn't need to capture the P12 group unless needed to prevent capture of a white group.RIGHT])(;W[sh];B[sg];W[rf];B[pg])(;W[sf];B[sg]))(;W[rf];B[qh](;W[sg];B[sh](;W[rh]C[It's ko in your favor, but you can do better.])(;W[sf];B[pg]))(;W[rh];B[sh])(;W[sh];B[sg];W[sf];B[rh])(;W[sf];B[sg]))(;W[rh];B[qh](;W[sg];B[sh];W[rf];B[sf];W[se];B[sg])(;W[sh];B[sg])(;W[sf];B[sh](;W[sg];B[rf])(;W[rf];B[sg]))(;W[rf];B[sh]))(;W[sh];B[sg](;W[qh];B[rh];W[rf];B[pg])(;W[rh];B[qh])(;W[rf];B[qh];W[sf];B[rh])(;W[sf];B[rf](;W[qh];B[rh])(;W[rh];B[qh])(;W[pg];B[qh])))(;W[pg]C[why would you do something like this];B[rf]LB[sf:miai]LB[sg:miai])(;W[sf];B[qh](;W[rf];B[sh];W[sg];B[pg])(;W[sg];B[sh];W[rf];B[pg])(;W[sh];B[sg];W[rf];B[rh])(;W[rh];B[sh](;W[sg];B[rf])(;W[rf];B[sg]))))