A simple little situation that surprised me when I first discovered it. It comes up often in tripod group variations.
Thanks to Bommel for finding the correct correct solution.
(;AP[goproblems]AW[qp][oo]AW[pq]AW[qo]AW[oq]AB[qq]AB[pr]AB[rq]AB[rp]AW[ro]AW[sp]AB[sr]AW[rs]AB[qs](;W[or];B[os]C[Black either escapes along the bottom, or gets a ko. It's a hard ko, to be sure, and a difficult crawl, but white can prevent both.])(;W[rr];B[or])(;W[os];B[or](;W[nr];B[rr];W[ns]TR[ps]C[Black can't play at Q1, and if he captures, white will play there to make a false eye. Good job!RIGHT])(;W[rr];B[nr])))