Key.isdown(key.LEFT) what is opposite of this?

onClipEvent (enterFrame) {
 if (key.isdown(key.LEFT)) {
 _x-= speed;
 }
 if (key.isdown(key.RIGHT)) {
 _x+= speed;
 }
 if (key.isdown(key.DOWN)) {
 _y+= speed;
 }
 if (key.isdown(key.UP)) {
 _y-= speed;
 }
}

i have all this code for my down buttons, but i want some more A/s for when my keys are not pushed…so its like the opposite, can you give me some examples?
-thanks