float dx = xCoord - receiver.xCoord;
float dy = yCoord - receiver.yCoord;
float dz = zCoord - receiver.zCoord;
if (dx * dx + dy * dy + dz * dz < 100 * 100) {
BlockIndex index = new BlockIndex(receiver.xCoord, receiver.yCoord, receiver.zCoord);
if (!targets.containsKey(index)) {
addLaser(receiver.xCoord, receiver.yCoord,
receiver.zCoord);