similar circumstance, then the unpaid portion of all remaining installments shall be due on the date of such event (or in the case of a title 11 or similar case, the day before the petition is filed). The preceding sentence shall not apply to the sale of substantially all the assets of a taxpayer to a buyer if such buyer enters into an agreement with the Secretary under which such buyer is liable for the remaining installments due under this subsection in the same manner as if such buyer were the taxpayer. (4) Proration of deficiency to installments If an election is made under paragraph (1) to pay the net tax liability under this section in installments and a deficiency has been assessed with respect to such net tax liability, the deficiency shall be prorated to the installments payable under paragraph (1). The part of the deficiency so prorated to any installment the date for payment of which has not arrived shall be collected at the same time as, and as a part of, such installment. The part of the deficiency so prorated to any installment the date for payment of which has arrived shall be paid upon notice and demand from the Secretary. This subsection shall not apply if the deficiency is due to negligence, to intentional disregard of rules and regulations, or to fraud with intent to evade tax. (5) Election Any election under paragraph (1) shall be made not later than the due date for the return of tax for the taxable year described in subsection (a) and shall be made in such manner as the Secretary may provide. (6) Net tax liability under this section For purposes of this subsection— (A) In general The net tax liability under this section with respect to any United States shareholder is the excess (if any) of— (i) such taxpayer’s net income tax for the taxable year described in subsection (a), over (ii) such taxpayer’s net income tax for such taxable year determined without regard to this section. (B) Net income tax The term net income tax means the regular tax liability reduced by the credits allowed under