Tax computed after application of credits against tax
For purposes of this section, the term “tax” means—
(1)#
the tax imposed by chapter 1 (other than any increase in such tax by reason of section 143(m)), plus
(2)#
the tax imposed by chapter 2, plus
(3)#
the tax imposed by chapter 2A, minus
(4)#
the credits against tax provided by part IV of subchapter A of chapter 1, other than the credit against tax provided by section 31 (relating to tax withheld on wages).