Cal. Code Regs. tit. 18 § 13692.6
A power which is exercisable only in conjunction with another person, and which after application of the rules set forth in Sections 13692.4 and 13692.5, above, constitutes a general power of appointment will be treated as though the holders of the power who are permissible appointees of the property were joint owners of property subject to the power. The donee under this rule will be treated as possessed of a general power of appointment over an aliquot share of the property to be determined with reference to the number of joint holders, including the donee, who (or whose estates or creditors) are permissible appointees. Thus, for example, if X, Y and Z hold an unlimited power jointly to appoint among a group of persons, including themselves, but on the death of X the power does not pass to Y and Z jointly, then Y and Z are not considered to have interests adverse to the exercise of the power in favor of X. In this case X is considered to possess a general power of appointment as to one-third of the property subject to the power.
NOTE: Reference: Section 13692, Revenue and Taxation Code.
Cal. Code Regs. Tit. 18, § 13692.6