Each United States shareholder of a controlled foreign corporation which for any prior taxable year was an export trade corporation shall include in his gross income under section
951
(a)(1)(A)(ii), as an amount to which section
955 (relating to withdrawal of previously excluded subpart F income from qualified investment) applies, his pro rata share of the amount of decrease in the investments in export trade assets of such corporation for such year, but only to the extent that his pro rata share of such amount does not exceed an amount equal to—