(5)
an amount equal to—
(A)
the tax for the taxable year computed without such deduction, minus
(B)
the decrease in tax under this chapter (or the corresponding provisions of prior revenue laws) for the prior taxable year (or years) which would result solely from the exclusion of such item (or portion thereof) from gross income for such prior taxable year (or years).
For purposes of paragraph (5)(B), the corresponding provisions of the Internal Revenue Code of 1939 shall be chapter 1 of such code (other than subchapter E, relating to self-employment income) and subchapter E of chapter 2 of such code.