Simplified from a game I played. How does B respond to the marked stone? I almost definitely missed some variations when I first put this up - if you spot one, please yell at me. ^^"
(;AW[rq]AW[qq]AB[qp]AB[rp]AW[pp]AB[pq]AW[oo]AW[on]AW[no]AW[mo]AW[pm]AW[qm]AW[qo]AB[nq]AB[np]AB[mp]AB[lq]AB[lr]AB[mr]AB[lo]AB[ln]AB[mn]AB[nn]AB[om]AB[ol]AW[nm]AB[pl]AB[ql]TR[rq]AP[goproblems]
(;B[ro];W[rn]
(;B[op]
(;W[pr]
(;B[oq]
(;W[sp];B[po];W[so];B[qn];W[rm];B[pn]C[not the best result - b has a chance at killing everything if he plays instead of p3])
(;W[po]C[W makes a mistake! How does b punish?]
(;B[qn];W[pn];B[rm]C[Lucky for you that w made a mistake - p3 is a mistake on its own, but you got away with it.RIGHT])
(;B[pn];W[qn]C[B lost the chance and the fight.])))
(;B[po];W[pn]
(;B[qn]C[Now b can kill the bottomRIGHT])
(;B[pp]C[RIGHT])))
(;W[pn];B[po]C[Two-step ko for w, two stage ko for b... probably w's best result.RIGHT]))
(;B[qn];W[pn];B[op];W[so];B[po]C[Ko for w's life probably the best result for w.RIGHT]))
(;B[op]
(;W[pn];B[po]C[A picnic ko for w's life.RIGHT])
(;W[pr];B[po];W[rr]C[Apparently the best way for w to play.RIGHT])
(;W[ro];B[po];W[sp];B[pp];W[pr]
(;B[rm];W[rr]C[RIGHT]))))