In the formula in the first paragraph,(a) A is the amount of the disability assistance payment;
(b) B is the amount by which the aggregate of all amounts each of which is the amount of a contribution made before the particular time to any registered disability savings plan of the beneficiary exceeds the aggregate of all amounts each of which would be the non-taxable portion of a disability assistance payment made before the particular time under any registered disability savings plan of the beneficiary if the formula in the first paragraph were read without reference to D;
(c) C is the amount by which the fair market value of the property held by the plan trust immediately before the disability assistance payment exceeds the assistance holdback amount in relation to the plan;
(d) D is an amount in respect of which a holder of the plan pays a tax under section 207.05 of the Income Tax Act (R.S.C. 1985, c. 1 (5th Suppl.)) in relation to the plan, or another plan for which the plan was substituted by the holder, thati. has not been waived, cancelled or refunded, and
ii. has not otherwise been used in the year or a preceding year in computing the non-taxable portion of a disability assistance payment made under the plan or another plan for which the plan was substituted.