§ 101-a. Taxable years to which tax applies; tax for taxable years
beginning prior to and ending after January first, nineteen hundred
sixty-six. (a) General.--The tax imposed by section one hundred one,
with any modification permitted by subdivision (b) of this section, is
imposed for each taxable year beginning with taxable years ending on or
after January first, nineteen hundred sixty-six.

(b) Alternate methods for determining tax for taxable years ending on
or after January first, nineteen hundred sixty-six.--(1) The tax for any
taxable year ending on or after January first, nineteen hundred
sixty-six and before December thirty-first, nineteen hundred sixty-six,
shall be an amount equal to the tax which would have been imposed had
section one hundred one been in effect for the entire taxable year,
multiplied by the number of months (or major portions thereof) in such
taxable year which occur after December thirty-first, nineteen hundred
sixty-five and divided by the number of months (or major portions
thereof) in such taxable year.

(2) In lieu of the method of computation of tax prescribed in
paragraph one, if the taxpayer maintained adequate records for the
portion of any taxable year ending on or after January first, nineteen
hundred sixty-six, and before December thirty-first, nineteen hundred
sixty-six, which falls within the calendar year nineteen hundred
sixty-six, the tax for such taxable year at the election of the taxpayer
may be computed on the basis of the unincorporated business taxable
income which the taxpayer would have reported had he filed a federal
income tax return for a taxable year beginning January first, nineteen
hundred sixty-six and ending with the close of such taxable year ending
before December thirty-first, nineteen hundred sixty-six. Such taxable
year beginning January first, nineteen hundred sixty-six and ending
before December thirty-first, nineteen hundred sixty-six, shall be
deemed (unless clearly indicated otherwise) to be the taxable year of
the taxpayer. For purposes of this paragraph two, the unincorporated
business exemptions allowable under section one hundred nine, the credit
allowable under subdivision (b) of section one hundred one and any net
operating loss deduction as modified pursuant to subdivision two of
section one hundred six shall each be reduced by the same part of such
exemptions, credit, or net operating loss deduction (as the case may be)
as the number of months (or major portions thereof) in the taxable year
occurring before January first, nineteen hundred sixty-six is of the
number of months (or major portions thereof) in such taxable year.
Except as provided in this paragraph two, the tax for such period ending
before December thirty-first, nineteen hundred sixty-six, shall be
computed in accordance with the other provisions of this title.