956. Notional dispositions.

Certain occurrences which may have the effect of transferring value out of a person's estate, but which under general law involve no disposition, are treated for inheritance tax purposes as involving a disposition1. Such notional dispositions occur:

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    (1)     where the value of a person's estate is diminished, and the value of another person's estate or of any settled property, other than settled property treated2 as property to which a person is beneficially entitled, is increased by the first-mentioned person's omission to exercise a right