Thank you to Morten's problem 379 for the pre-game practice.
(;AB[ja]AB[jc]AB[ib]AB[jb]AB[kb]AB[lc]AB[mc]AB[nc]AB[nb]AB[ob]AW[pb]AW[pc]AW[oc]AW[nd]AW[md]AW[ld]AW[kc]AW[kd]AW[jd]AW[ic]AW[hc]AW[hb]TR[jb]C[Black just played the marked stone. Can white punish that mistake?]AP[goproblems]
(;W[la];B[ma]
(;W[lb]
(;B[oa]C[CHOICE];W[pa]C[Well done! Black cannot approach from either side.RIGHT])
(;B[mb];W[oa]C[RIGHT]))
(;W[oa];B[lb]))
(;W[ma];B[la]
(;W[oa];B[na])
(;W[na];B[oa])
(;W[mb];B[sa]C[Black plays elsewhere.];W[oa];B[lb]))
(;W[oa];B[la]
(;W[ma])
(;W[na];B[ma])
(;W[mb];B[sa]C[Black plays elsewhere.]
(;W[na];B[lb])
(;W[ma])))
(;W[lb];B[la]
(;W[ma];B[mb])
(;W[oa];B[na])
(;W[na];B[oa]))
(;W[pa];B[la]
(;W[oa];B[na])
(;W[na];B[oa])
(;W[ma];B[oa]))
(;W[na];B[la]
(;W[oa])
(;W[ma])
(;W[mb];B[ma]))
(;W[mb];B[la]
(;W[oa])
(;W[na])
(;W[ma])))