ChrisSchack: I think the first move has to be here, it seems like the vital point. It's both a peep at a and the eye-stealing tesuji in conjunction with b.
W has 4 liberties to 2 (maybe 3 to 2 for other placements of 1) and kills the cut stones, and with them the group.
Now W just has to connect out, and unless B plays a sagari, W simply pushes through.