(I tried to explain and cover the correct path(s), I'll add more wrong paths later - Don't try to solve it if you want to know why u failed.. in case u do, that is;)
It's not that it's the first time I see it but from now on I'll never forget.. :)
(;AB[bn]AB[cn]AB[co]AB[dp]AB[dq]AB[fq]AW[bo]AW[cp]AW[cq]AW[bq]C[It's a wonderful tsumego. Surely anyone can find the obvious ko but can you do better - Can you kill ***unconditionally***?]AP[goproblems]
(;B[ds]
(;W[cr]C[Landing with a tobi? Your mind works in a misterious way... ;)]
(;B[ar];W[ap]
(;B[an]C[Well done! The tobi (D1) is indeed a spectacular move making the two 1x2 points miai, rendering whites resistance futile.CHOICERIGHT])
(;B[aq];W[br]C[White lives! And you were sooo close... How could you fail afer D1? ;(])
(;B[bs];W[cs]C[White lives! And you were sooo close... How could you fail afer D1? ;(])
(;B[cs];W[bs]
(;B[an]C[Well done! The tobi (D1) is indeed a spectacular move making the two 1x2 points miai, rendering whites resistance futile.RIGHT])
(;B[dr];W[aq]C[White lives! And you were sooo close... How could you fail afer D1? ;(])))
(;B[cs];W[bs]
(;B[ar]C[Well done! The tobi (D1) is indeed a spectacular move making the two 1x2 points miai, rendering whites resistance futile.RIGHT])
(;B[ao];W[ar]C[White lives! And you were sooo close... How could you fail afer D1? ;(])
(;B[ap];W[ar]C[White lives! And you were sooo close... How could you fail afer D1? ;(])
(;B[aq];W[ar]C[White lives! And you were sooo close... How could you fail afer D1? ;(])
(;B[an];W[ao]C[White lives! And you were sooo close... How could you fail afer D1? ;(]))
(;B[ao];W[ap];B[bp]MA[bo]C[A very hard ko for white but it's still a ko! And you were sooo close... How could you fail afer D1? ;(])
(;B[ap];W[ao]C[White lives! And you were sooo close... How could you fail afer D1? ;(])
(;B[aq];W[ar]C[White lives! And you were sooo close... How could you fail afer D1? ;(])
(;B[an];W[ao]C[White lives! And you were sooo close... How could you fail afer D1? ;(])
(;B[bs];W[cs]C[Only thing black can get now is a ko.. And you were sooo close... How could you fail afer D1? ;(]LB[ao:1]LB[ap:2]LB[bp:3])
(;B[dr];W[ar]C[White takes the key point and lives! And you were sooo close... How could you fail afer D1? ;(]TR[bs]TR[ap]))
(;W[ap]C[Landing with a tobi? Your mind works in a misterious way... ;)]
(;B[bs];W[br]
(;B[ar]C[Well done! The tobi (D1) is indeed a spectacular move making the two 1x2 points miai, rendering whites resistance futile.CHOICERIGHT])
(;B[an]C[Well done! The tobi (D1) is indeed a spectacular move making the two 1x2 points miai, rendering whites resistance futile.RIGHT]))
(;B[an];W[bs]
(;B[ar]C[Well done! The tobi (D1) is indeed a spectacular move making the two 1x2 points miai, rendering whites resistance futile.RIGHT])
(;B[br];W[cr]
(;B[ar];W[ao]C[White lives! And you were sooo close... How could you fail afer D1? ;(])
(;B[ao];W[ar]C[White lives! And you were sooo close... How could you fail afer D1? ;(]))
(;B[cr];W[br]
(;B[ao];W[ar];B[bp]C[Still a ko.. And you were sooo close... How could you fail afer D1? ;(]MA[bo])
(;B[ar];W[ao]C[White lives! And you were sooo close... How could you fail afer D1? ;(]))
(;B[ao];W[ar]
(;B[bp];W[cr]C[White lives! And you were sooo close... How could you fail afer D1? ;(])
(;B[cr];W[br];B[bp]C[Still a ko.. And you were sooo close... How could you fail afer D1? ;(]MA[bo])))
(;B[ar];W[cr]
(;B[an]C[Well done! The tobi (D1) is indeed a spectacular move making the two 1x2 points miai, rendering whites resistance futile.RIGHT])
(;B[cs];W[bs]
(;B[an]C[Well done! The tobi (D1) is indeed a spectacular move making the two 1x2 points miai, rendering whites resistance futile.RIGHT])
(;B[aq];W[br];B[an]C[Well done! The tobi (D1) is indeed a spectacular move making the two 1x2 points miai, rendering whites resistance futile.RIGHT])
(;B[br];W[ao]C[White lives! And you were sooo close... How could you fail afer D1? ;(]))
(;B[bs];W[cs]C[White lives! And you were sooo close... How could you fail afer D1? ;(])
(;B[aq];W[br]C[White lives! And you were sooo close... How could you fail afer D1? ;(]))
(;B[br];W[cr]
(;B[cs];W[bs];B[as];W[ar];B[aq]C[Still a ko.. And you were sooo close... How could you fail afer D1? ;(])
(;B[bs];W[cs]C[White lives! And you were sooo close... How could you fail afer D1? ;(])
(;B[ar];W[bs]C[White lives! And you were sooo close... How could you fail afer D1? ;(])
(;B[an];W[ao]C[White lives! And you were sooo close... How could you fail afer D1? ;(]))
(;B[cr];W[br]C[White lives! And you were sooo close... How could you fail afer D1? ;(])
(;B[cs];W[br]C[White lives! And you were sooo close... How could you fail afer D1? ;(])
(;B[dr];W[br]C[White lives! And you were sooo close... How could you fail afer D1? ;(])))
(;B[dr];W[ap]
(;B[br];W[cr];B[cs];W[bs];B[as];W[ar];B[aq]C[Only a ko..])
(;B[cr];W[br]C[White lives!])
(;B[ar];W[br];B[bs];W[cs];B[cr];W[as]C[Only a ko..])
(;B[cs];W[br]C[White lives!])
(;B[bs];W[br];B[ar];W[cs];B[cr];W[as]C[Only a ko..])
(;B[an];W[ao]
(;B[br];W[cr];B[cs];W[bs];B[as];W[ar];B[aq]C[Only a ko..])
(;B[bs];W[br];B[ar];W[cs];B[cr];W[as]C[Only a ko..])
(;B[ar];W[br]C[White lives!])
(;B[cr];W[br]C[White lives!])
(;B[cs];W[br]C[White lives!])))
(;B[ao];W[ap];B[bp]MA[bo]C[Well it is the obvious ko, which isn't good enough! Unconditional kill is possible!])
(;B[cr];W[br]
(;B[ao];W[dr]C[White lives!])
(;B[dr];W[ap]C[White lives!])
(;B[ap];W[dr]C[White lives!])
(;B[ds];W[ap]C[White lives!])
(;B[cs];W[bs]
(;B[dr];W[ao]C[White lives!])
(;B[er];W[ao]C[White lives!])
(;B[ds];W[ao]C[White lives!]))
(;B[bs];W[dr]
(;B[ds];W[er]C[White lives!])
(;B[cs];W[er]C[White lives!])
(;B[er];W[cs]C[White lives!]))))