John Hunter is the sole owner of Deerfield Corporation and Elkton Corporation. Both Deerfield and Elkton are regular C Corporations that file Form 1120. Elkton loses a U.S. government contract that is the primary source of its income. As a consequence, it faces a serious cash flow problem. Deerfield advances Elkton $500,000 to cover its cash flow problem. Two characteristics of the advance are: (1) no fixed maturity date, and (2) interest payments are contingent on Elktons future profitability. Eighteen months after Deerfield makes the advance, Deerfield determines that Elkton never will be able to repay the advance. Deerfield claims a $500,000 business bad debt deduction on its 2019 corporate tax return. On later audit, the IRS disallows Deerfield the business bad debt deduction it claimed on its 2019 return. The IRS insists that there are different federal income tax consequences of the uncollectible advance that Deerfield Corporation made to Elkton Corporation. What authorities should be used in this research problem?