At a certain time k, two universal life policies have exactly the same account value, death benefit, premiums, expenses and cost of insurance rates. In both cases the cost of insurance discount rate is the same as the credited interest rate. One policy is type A and the other is type B. Show that the difference between the type A and type B account values at the end of the year is the same as the difference between the type B and type A COI for that period, accumulated with interest to the end of the year.