My first problem. I think it is very easy but maybe it is a good work for begginers. Sorry if such a problem already exists. Thank you to Larsen, tails, davidgoto and Winnetou2 for the comments !
(;AB[se]AB[re]AB[qe]AB[qd]AW[sd]AW[rd]AW[rc]AW[qc]AB[pc]AB[oc]AB[ob]AW[pb]AW[oa]AW[qa]AB[nb]AW[od]AB[oe]AB[mc]AB[ld]AB[le]AB[sb]C[White to the best result.]AP[goproblems]
(;W[rb]
(;B[na]
(;W[pa];B[ra]C[];W[sa]C[White needs to win this ko.RIGHT])
(;W[sc]
(;B[pa]C[]
(;W[sa];B[qb]C[Not the good way.])
(;W[ra]
(;B[qb]C[Not the doog way.])
(;B[oa]))
(;W[qb];B[sa]C[Not the doog way.]))
(;B[sa];W[pa]C[RIGHT]))
(;W[ra];B[pa]C[Not the good way.])
(;W[sa];B[ra]
(;W[pa];B[qb]C[Not the good way.])
(;W[qb];B[sa]C[Not the good way.])
(;W[sc]
(;B[pa];W[sa];B[qb])
(;B[qb])))
(;W[qb];B[sa]C[Not the good way.]))
(;B[ra]
(;W[sa];B[na]
(;W[sc];B[pa]C[];W[qb]C[White live with 1 sacrificed stone.])
(;W[pa];B[ra];W[qb];B[sc]C[Not the good way.]))
(;W[sc]
(;B[na]
(;W[sa];B[pa];W[qb]C[White live with 1 sacrificed stone.])
(;W[qb];B[pa]))
(;B[qb]C[Not the good way.])))
(;B[sa]
(;W[pa]
(;B[ra];W[sc];B[sa])
(;B[na];W[ra]))
(;W[ra];B[na];W[pa])))
(;W[sa];B[rb]
(;W[ra]C[White can't have two true eyes anymore !])
(;W[qb]C[White can't have two true eyes anymore !]))
(;W[ra];B[rb]C[Not the good way]
(;W[qb]C[White can't have two true eyes anymore !])
(;W[sa]C[White can't have two true eyes anymore]))
(;W[qb];B[sa]C[Not the good way !])
(;W[sc];B[rb];W[qb]
(;B[ra];W[sa];B[rb];W[ra];B[na];W[sb];B[pa]C[Not the good way !])
(;B[na]C[Not the good way !])))
