Homo simply meaning highest occupied molecular orbital, and lumo, meaning lowest unoccupied molecular orbital. So if we go back to the first step in this additional reaction, we see that our homo, the highest occupied molecular orbital, is the pi bond. So this is our lowest base. And in this case, our lowest unoccupied molecular orbital is the antibonding Sigma Bond. Remember, the bonding Sigma Bond is completely filled. The antibonding has no electrons, and so that means it must be the lowest unoccupied molecular orbital.