In Chapter 12 bankruptcy proceedings in which the debtors proposed treating a capital gains tax on the postpetition sale of their farm as an unsecured claim to be paid to the extent funds were available, with the unpaid balance being discharged, the objection of the IRS is sustained, as the federal income tax liability resulting from the sale was not "incurred by the estate" under section 503(b) of the Bankruptcy Code, and thus was neither collectible nor dischargeable in the Chapter 12 plan.