Initially, the first container has only alcohol, and the second has only water. After transferring the cups as described in the problem, both containers will have some proportion of alcohol and water. The total amount of liquid in both containers remains constant, and the quantities of alcohol and water are just being transferred between the containers.
The operations result in a balance between the proportion of alcohol in the first container and the proportion of water in the second container. Therefore, \( A = B \).