Problem with NPCS

programming flash
1

I have this code to initialize NPCS in my game if you’re in their sight range

onClipEvent(load) {
    working = false;
    sight = 40;
}
onClipEvent(enterFrame) {
    if(_level0.guy._x - this._x < sight and _level0.guy._x - this._x > -sight and _level0.guy._y - this._y < sight and _level0.guy._y - this._y > -sight) {
        working = true;
    }
    if(working == true) {
        trace("Working");
    }
}

Anyone know why its not working?