ProtoDeuteric: takees the corner eye away, and white is either too slow or lacks the liberties necessary for a proper response. I think "a" is also possible, but there is potential ko considerations that make the situation more messy than it needs to be.
togo: If here, then kills by leaving only one eye.
Anonymous: leads to ko. If white wins the ko, she will capture and live with two eyes at and . If black wins the ko, he will connect at the marked spot and thereby kill the white group.