660. For the purposes of section 659, the allocable amount for a preferred beneficiary under a trust in respect of the trust for a taxation year is(a) where the trust is, at the end of the year, an alter ego trust, a joint spousal trust, a post-1971 spousal trust or a pre-1972 spousal trust and a beneficiary, referred to in subparagraph a of the first paragraph of section 653 or in the definition of “pre-1972 spousal trust” in section 652.1, is alive at the end of the year, an amount equal to the trust’s accumulating income for the year, if the preferred beneficiary is a beneficiary so referred to, and, in any other case, nil;
(b) where paragraph a does not apply and the preferred beneficiary’s interest in the trust is not solely contingent on the death of another beneficiary who has a capital interest in the trust and who does not have an income interest in the trust, the trust’s accumulating income for the year; and
(c) in any other case, nil.