In any case where—
part only of a holding of qualifying investments is comprised in a person's estate, and
investments included in that holding are sold by the appropriate person within the period of twelve months immediately following the date of the death,
this Chapter shall apply as if the entirety of the holding were comprised in the estate and, if a claim is made in respect of the investments referred to in paragraph (b) above, the taxable fraction of the value of the investments to which the claim relates, as determined under this Chapter, shall be the value of that part of those investments which is comprised in the estate.
In subsection (1) above, "taxable fraction" means the fraction of which the numerator is the value, as determined apart from this Chapter, of the part of the holding referred to in paragraph (a) of that subsection and the denominator is the value, as so determined, of the entirety of that holding.