(;AB[pc][qc][rc][sc][ob][nb][mc][md][me][kb]AW[pb][qb][rb][sb][oc][od][oe][pe][qe][re][se][nc]SZ[19]C[Black plays.

Source:
    Just one among dozens of the author's embarrassing moves at the 2010 Go Congress in Colorado Springs.]

(;B[ra]C[I slapped this stone down after only a few seconds thought.  BIG mistake!]
(;W[qa]C[The game line.  White returns the favor!];B[oa]C[Black finally wakes up.];W[mb];B[lb];W[pd];B[ma]C[Black wins the semeai by a move.])
(;W[oa]C[White should have played sente here to gain a move in the semeai.];B[mb]C[Black has to defend.];W[pd];B[na];W[qd];B[pa];W[rd]C[White saves his corner stones.]))
(;B[pa]C[Black should have played here.];W[qa];B[ra];W[oa];B[mb];W[pd];B[na];W[qd]C[And Black takes 1st in a ko worth almost 25 points.])
(;B[qa]C[Also fails.];W[oa]C[Sente against the 2 stones.];B[mb];W[ra]C[White lives outright and Black's 4 stones die.]))